Are you looking for a Sport or 'just' a 325i four or two door? They are already 'proper' classic for the most part as they started making them in 1982 and stopped in 1990, so even the youngest is nigh on 20 years old now - barring the cabriolets, which they made until '93 - but even so...
Pitfalls are knackered suspension components from age, worn interiors, cheap 'mods' done by previous owners, rust, shot head gaskets and warped cylinder heads. Rest is just general 'old' car stuff really. Buy a good one with history and it'll be just fine - buy one that's been abused or hacked about and it'll just be a pain. Parts are relatively cheap and easy to get hold of from the likes of ECP and GSF, plus BMW dealers still quite happily service and maintain E30s. Quite easy cars to work on as well, although the cambelt can be a bit of a chore to replace.
BMW dealers can help you with the original specifications and service history if there's little left, or it's missing. They won't give you specifics unless you own it but my local one will quite happily entertain 'general' enquiries about history if you're polite.
My old one, a 325i SE:
Fantastic bits of kit.
[TW]Fox;15491409 said:
E30 325i's are the most overated BMW in the universe and are scene taxed to **** as a result. You'll spend 5k on a car that will give you the ownership experience of a 100 quid banger, constantly fighting the rot and bits falling off what is a 20 year old car thats normally been driven hard its entire life.
Admire other peoples E30's instead
Or use the money to buy your 530d
Funny, and I know what you mean - but I'd dispute that. You can buy an exceptionally nice sport for about 2-3k that will be reliable and not require much outside of routine maintainence, or a really nice four door or iS for 1-2k that will be in excellent condition. Only suckers believe, or pay, scene tax prices and end up with knackered old nails that haven't seen any love.
One question though, how are they overated? People love them because they're light, simple, great fun to drive and rewarding to own. I wouldn't say they were overated

Certainly the cooking spec 316s and 318s aren't much to write home about but a clean example of either is still a charming, fun and reliable daily car, to say the least.
I know mine was the less desirable four door but hell, that only cost me a grand, didn't have any rust barring a few paint blisters and nothing ever went wrong or fell off. I drove it for 6 months, put 5000 miles on it and all it ever needed was an oil change and some plugs.....Lovely car to drive too.
Even sold it for 500 quid more than it cost originally when the time came to move it on. Not a net profit by any means but a decent return on the initial purchase price!

If you look after it, its value will remain the same, or increase, although that depends on how good you are at selling it at the end of the day