Agree with the post above, upfront cost for an evo is not too bad but if you get hooked on aftermarket stuff your looking at anywhere from $10-$30k.
As for the evo as a second car i think it's great. I used to have an old jetta for a dd and the evo as a second car. The one thing I hated was not having a garage for it so I would take it to a parking lot and park it there, haha. Currently the jetta slipped a tooth and is a gonner but I travel for work and the evo is still my weekend car, haha. I've had no problems with it sitting at the airport for weeks and starts up no problem each time.
Another thing is that when you dd the evo, you get more used to the manual tranny and are a little easier on it. Now when it's a weekend car it's like getting back into a new car again. Not really but you get the point.