I'm going to get Continental DWS for my all-seasons... they're phenomenal tires.
+1 on the Conti DSW's. I have been running them for the past few winters and beyond getting some dedicated snow tires, I believe the DSW's are hands down the best all season's out there.
I couldn't believe the difference when I first got them.
1) They are quieter than the OEM tires.
2) I actually got 2 mpg better with these tires.
3) In the winter on the OEM Goodyear's, the traction control would always kick in, rain or snow. In fact, I dreaded even an inch of snow. The Goodyear's had no traction at all. After installing the Conti DSW's, the traction control rarely if ever came on. That's how good these tires are.
So if you haven't bought all seasons yet, take a serious look at the Continental DSW Extreme Contact.
As for autocross tires, I think I'll go for the RS3s. That is the tire that the fastest Mazda3 driver runs in my region(he is stupid fast), that is what another hotshoe Mazdaspeed3 driver runs(though I haven't talked to them), and many other "heavier" cars like BMW 3 series and a still run the RS3.
A lot of people are jumping to the BFGs and everyone I've talked to has liked them... but not been super impressed with them(one on an 08ish Civic SI, and someone else on another BMW). Granted, they're not pros or anything, but they're some regularly top 20% drivers... in my region that's doing pretty damn good.
Between Star Specs, BFGs, RS3s, and RE-11As you can't go wrong.
I'll probably go for the RS3s because I don't want an inside-outside tire, and I've heard the RS3s are easier to drive fast, while the Star Spec ZIIs are more "peaky" and they break away at the limit and you need to overcompensate considerably to bring them back to "grip" again either by slowing down or reducing steering angle depending on if it's over or understeer... it's supposedly not a linear breakaway like some other tires.
I am curious about the RE-11As because nobody seems to give them a thought, whenever I buy I'll probably just get whichever is the best deal and happens to be in stock.
Regarding track tires, I have been running the Direzza Star Specs ZI's as both my summer and track tires. They are very loud and the next set will strictly be for the track. As a whole, I really like these tires. I have done well with them but I agree with flatlander's observations. Let's just summarize by saying the ZI's are very capable tires but require more skill to get the most of them. Where they excel is by being both a daily tire, including heavy rain, and a track tire. Also note, I don't have any direct experience with the ZII's but I here they are much improved.
If you intend to run these tires strictly on the track, I would recommend the Kuhmo's. The only downside is they require a lot of heat to be sticky but when it's hot they stick like glue.
Another suggestion as well. You mentioned going to a 16" rim. It's a good idea, especially for AutoX. However, I wouldn't recommend a shorter sidewall (low profile). If your still new to AutoX, running a lower profile tire will not be forgiving. You will reach peak grip much more quickly and may be likely to spin out. I'd still go with a 16" or maybe a 17", just don't go low profile unless you are very comfortable driving at the limits.
I have been doing this and it's working for me, but at times it can be really scary.