I only have a few thousand miles but I feel the same. It took me about three miles to overcome the initial twitchiness. My "crap" Kenda tires seem to work just fine and I enjoy tossing the Spyder around turns fast enough to annoy the nanny, although I may change them when I enter Formula One. When I read this thread, I wonder WTH is wrong with me?!?
Actually I think some people are simply more sensitive to the feeling of the Spyder than others. Some also ride enough that they develop greater sensitivity. Also in every forum like this there are some who feel they know more than the engineers who designed the machine. Maybe they are wrong, maybe they are right, I don't know or care.
Many of these suggestions are for and from advanced folks who can fine tune it and actually tell the difference. Their suggestions are probably really good for THEM but irrelevant to beginners like me and Easy Rider who wouldn't know the difference. If the alignment and tire pressure are correct as intended by the factory and you still aren't comfortable, I'd say the problem is primarily in the Rider (no offense intended, we are all different). If so, I'd say to forget the other suggestions and get a different machine.