One guys $.02, certainly worth less than that, and I'm sure that others wil chime in after the holiday.
You'll hear that tires are the most important component. I think it is that grey matter between your ears.
You'll hear that buying the best tires you can afford is the safest. I think that leaning to identify problems and adapt is the best skill you can have when riding on the street or the track.
With consistently good body position, you can ride around a LOT of other issues. One of my most clear memories of track day riding was being pretty zippy around NHIS, now NHMS, on my old 400...then seeing one of the Wood brothers go out on a bone stock s%&$box EX500 (which are build of hinges, if you've never ridden one) 5 seconds a lap faster than I was going.
I ride my best (safest and fastest) on nearly worn out tires. This is not advice for you or anyone else, but knowing precisely how the bike is behaving and being able to modify my style to suit that is where I'm the happiest and feel like I've done the best job. Having the skill to be able to always find and not go over "the limit" for the cirsumstances you're in may be the best tool in your skill toolbox.
If you are bumping against the limits on your current tire brand/model, I'd ask what you're doing about it. (I've ridden many track miles on ST tires. They give up pretty fast once they get warm (so you won't be running A pace on them), but can still go just fine as long as you stay within their limits...so you'd have to understand the limits of the package...you, bike, tires, etc.). You already mentioned body position, and you're spot on there. Good adaptive body position can transform your riding experience, regardless of what bike/tires you're on. How about that suspension? Is it set properly for you? And monitoring and adjusting tire pressure shouldn't be dismissed either, but you'll likely have a hard time finding the right setup for ST tires in a track day environment. You may be on your own to experiment with that if you stay on ST tires.
Tires that are worn out are likely not consistent from side to side (arc). This causes two things. First, as you lean the bike, you'll be going from high spots to flat spots. This can be unnerving to "feel" but also causes varying grip...not ideal. Second, this area of the tire will not hold heat like a new tire, so you can get cool spots...varying grip.
My recommendation is to try another model, since yours are worn out. I'm a Dunlop guy, but many good brands and models exist today, and they're phenominal compared to not that many years ago. Pirelli is also very popular and well loved. If you're doing pretty well on ST tires, I'd say make the move to a good street tire before moving to a Hypersport or race rubber. Get to know those, and monitor grip/wear, and then adjust your plan from there. At some tracks, I've gone faster on a Q3 rear than on my race tires. And surely talk to other SV guys and the tire vendors to make an informed decision, as I do not have many miles on an SV and have limited experience on non-Dunlop products.
I hope that this is somewhat helpful and to catch up at a track in the future!
