You should really post this in the e30 section but I can give you a quick basic run down as I've owned a few over the years with the current one in my stable for the last 3.5 years. Any car '88 and newer is and will be subject to emissions tests for the life of the car. '87 and older no emissions test whatsoever.
Insurance if you're over 25 with a reasonable driving record is not a problem.
Engine swaps are more difficult. Some that I know, just didn't tell their insurance company, but everyone knows if something happens, and their insurance company didn't know they don't have to pay, or they will and drop you. Once dropped good luck finding insurance elsewhere. Some insurance company's will cover you, others will charge a premium. So you have to pay due diligence shopping for insurance. Again, being older with a clean record pays dividends when it comes to this aspect. I'm 38 so there you go.
Reliability, cost of ownership, fun to drive, fuel economy, and all out joy of ownership are hard to beat. Cheapest car I've ever had to fix, run, beat, abuse and what not, a complete joy to drive. Plus the amount of high 5's I get from other motorists, the sheer number of people that try to pull me over and offer me to buy it is just astounding. I say if you want to pay too much for it it's yours! LOL, but I'm likely to never sell it!