I'm looking for a car that has a few more options than the E30 (tilt, cruise, power sunroof, etc) and maybe the E36 is it. I want to keep the same engine.
First off, you can quite easily get or retrofit an E30 with all of the above.
My brother had an E36 318iS. I still have my E30 iS. The E30 wins on fun to drive, character, and looks. These things matter to me. The E36 is a better cruiser, more refined, quieter etc. Comes down to what you want out of a car.
I have a second car (E30 318iS Touring with Cruise/AC/Computer/Heated Leather!) to do the mundane stuff. The iS Coupe is the car I'm closest too.
I can't see how the E36 can beat an E30 if you're truly a car nut, it just doesn't quite get you in the gut. The E36 is still an awesome car but London is rife with them and they are easily mistaken for Toyota's!
If you had to go get an E36 surely you'd have to look into the 2.5L 323i/6 or the 2.8L 328i/6. Why stick with the M42/M44 in a bigger, heavier car?
The 4 pot suits the E30 very well. The E36 has nicer engines in it's range including a decent 2.5L Diesel so for me, more engine choice would be the only reason to go there.
To be honest, there is no wrong decision here!