Henri - i think that the speedway front wings were the only effective way of rebalancing the car during the race - as you will know this happened very frequently, and the cars had mechanic adjustable wing incidence adjusters fitted to the nosebox.
This was linked to the wing crosstube. i think later (certainly by 88) the left and right wings were individually adjustable. they certainly were at Hemelgarn where i was. So removing the wings would not have been an option. My recollection is that they did not produce very much downforce - something that would come as no great surprise when you look at them. They are very close in size to those fitted to the 126C2 actually - so this reply is almost back on topic!
There are other guys who post here (Nigel Beresford would be the one) who had far more experience at the speedway than i had, and they could give you more detail.
I think that the story about Tom and the rear wing is correct - infact somewhere i think i have seen a picture of the car without the wing.
I cant remember the specifics, and by 88 the tunnels were a lot smaller, but very often running a very small rear wing at the appropriate height would energize the tunnels - literally suck the air out of them - and the net effect was a more aero efficient package than removing it - exactly the same principle applied on the LeMans cars i was involved with.
Peter