The 94+ tails clean up the rear end, so that's almost a necessity. Some people don't like them, but I think they're great.
Get some OEM clear corners. I don't really like those diamond aftermarket clears. I dunno, they just don't look right. I use amber bulbs in mine for a stock appearance and to keep from getting fix-it tickets.
My dad laughed at me when he saw me putting the OEM clears in, but after he saw what they looked like, he asked how much they were for his white N/A.
It just makes the front end look so much cleaner and modern.
An MR2s rarity will depend mainly on where you live. In some parts of Southern CA, they're everywhere. In other cities, like mine, you hardly see anyone else with one.
Don't go for huge rims/tire combos that'll bog your 5S down. That limits you quite a bit. I have 225/60/14s on my rears, and I totally feel the difference from 205/60. High mileage motors suck.