How will reducing the overall wheel/tire circumference from a little over 25" to about 24.5 affect performance (acceleration)?

 

You'll have slightly lighter weight (how much depends on whether you get a smaller wheel or not, whether it's a different wheel, etc.), and the smaller circumference will be like putting a slightly shorter gear in the rear end. In other words, at the same speed in the same gear, you will be turning higher rpms.

This will help you launch better in first gear, but you lose top end speed (not that that is a real concern for street cars). Your shift points will be at lower speeds, but the only place where this will make a difference is on a 0-60, 1/8, or 1/4 mile run, where you might introduce an extra shift during the run (which might negate the launch improvement you gained).

In the end, there isn't too much to be improved in the realm of acceleration, and what little improvement there is, will have little difference on the street.

---jps

P.S. You'll also dork up your speedo.