while i don't claim to be an expert in F1, i'll list my reasons why 'THIS TIME' kimi to ferrari will work
1. as
Cyanide mentioned, kimi is not the driver that left 2009 for rallying, he was exhausted mentally by the politics and i assume by
F1 in general. also, even though many will not agree on this, but
he did hit the bottom point of his form at that time. since his comeback, he is more relaxed and focused. i'd also say (IMO) his reflexes and concentration improved after his venture in WDC, that is one of the reasons why he fared better than schumi. he demanded more from the team (unlike first ferrari stint) and made the team listen to his requirements. Also, this is just my opinion by i believe Ferrari took a notice of how
LotusF1 let kimi be his own, saw how to manage him and how to extract the absolute best out of him.
2. Admit it or not, Ferrari does need a
good (and equal) no#2 driver. Yes, as long as we can remember ferrari has always employed a clear no#1 and no#2 driver , but most of the times those no#2s had been talented and able to finish close and often ahead of their main man (take for example RB, Irvine). but it was the management decisions of Jean Todt and Ross brawn that assured that the no#2 driver be kept under control when things went out of hand (i.e same as malaysia 2013 NR vs LH in MGP

).
However, the current administration of Ferrari under SD seems to think that with the current competitiveness of F1 grid and the points system, not to mention the economic situation (yes even for ferrari), it is better to have 2 no#1 drivers and let the natural order set in by 3/4th of the season. by then, one contender will emerge and the team can then persuade the other to co-operate. but in the mean time, due to each driver pushing the other to become WDC, they'll propel team in a good position in WCC (where the money comes from). MClaren has always worked in that principle and RBR has shown how it can be managed (even with skirmishes like isanbul/ multi 21 etc/FW saga). kimi will be the perfect addition to the 'new ferrari' in that he's the most non-political driver in the grid, give him a car and he'll drive. he wont come 3 hrs before the race and stay 3hrs after to make fuss. even alonso has to admit that off all the tier 1 drivers, kimi will make life least miserable.
3. since his carting day, kimi's ability has always been to judge the grip of the track, minimize wheel spin and scrub the least amount possible. that is one of the reasons he need a very sensitive steering, he doesn't like to fight with it (like Alonso who prefers understeer). this is one of the major reason that he has shined in the 'Pirelli era' (also why he suffered in 'bridgestone' era). Now, with the introduction of turbo and corresponding increased torque, driver abilities like kimi's will be even more valuable come 2014.
4. again, despite what the critics and haters say, kimi is one of the most talented
'car developer' and
technical persons in modern F1. yes, he speaks very little, but what he speaks is the exact reaction of the car. if he says the suspension is bad, it is bad. (for his liking at least). There has been countless quotes as to how how he can do wonders with setup and doesn't rely heavily on race engineers to set up his car (as long as the team listens to his changes) to make it fast. (
see my sig 
). there also has been quotes from personnel within ferrari, robertson and slade that why he suffered in 2008 as the team didn't listen to his demands earlier in the season and made the car to Massa's liking.
5. Ferrari has always opted for slightly aged drivers, who are
at their best, sometimes at there
twilight. they know the value of a battle hardened fighter (or aged cheese/wine

) and how sometimes the best years are the years towards the last 3/4 years of there career. (JB/MS/FA) kimi makes sense cause he's battle hardened, seen it all, been there done that and he knows he has to do it within the last best 3/4 years of his career.
6. obviously, kimi and ferrari knows each other, while it's always a risk to take a young guy at the beginning of a major rule change era, appointing kimi will remove that factor from the equation, he'll fit in just fine (like he did with LotusF1). ferrari will know his preferences, like steering setup, suspension setups etc
7. this point seems to have 'swept under the floor' due to the excitement, but we also need to remember that the last driver that James Allison has worked closely is not Fernando Alonso, but kimi raikkonen. he knows how kimi likes his cars, he knows kimi's strengths and how to extract them, his steering preferences and specially how to set the front end of the car to make him competitive in Qualifying (which had been his achilies heal during his last stint with SF and after his return). it'll be easier for James to work with kimi from the get go, specially seeing how he's to take more control of the development direction of SF from 2014. it'd be naive to discard the notion that james allison did have some influence in SF choosing kimi or vice versa, kimi to choose SF.
8. kimi will have his freedom within the team, he'll be able to go rallying (which both RBR and Lotusf1 denied), he'll be payed a fortune for his services and he'll have to control to choose his contracts. as we all know from LotusF1 stint that A Happy Kimi is a Fast kimi
9. kimi's consistency in grabbing points will increase Ferrari's ability to win the WCC and more often than not rattle RBR's nerves. with FA and KR on board, ferrari will have the 'Senna and prost' of modern F1, one with aggression, other with the long term consistency. once Ferrari finds the sweet spot of working with there drivers and win championships (even only the WCC), they'll have the continuity to push for consistency and improvements in the coming consecutive years and perhaps break the stranglehold of RBR on the championships.
10. finally, kimi will give the team much
publicity boost (if they need any

) within the Formula 1 fan demographic and in italy, for quite a while now ferrari and it's relationship with it's drivers, it's performance on track and it's management has been under scrutiny, by appointing kimi, they are poised to become the most talked about team within the paddock,
tifosis love kimi, italians love kimi, his unique personality was used by LotusF1 in a clever, humorous and effective way and certainly Ferrari will be exploit that too.
kimi now is way way more popular than kimi 2007-09, it'll be a positive boost for the
morale of the team.