Some SLK's and W202 C230k's have been using a pulley for over five years, and there seems to be no problems with premature engine wear. Someone posted on another board that instead of the engine lasting 200,000 miles maybe it will last for 190,000.
So far there is no ECU upgrade that does much. Renntech is working on one. You don't have to change the intercooler, but a more efficient one would help. A prototype has been built by Spearco, and is being tested.
Spearco Intercooler
As for the warranty, you can expect it to be canceled if anything happens to the engine. The Moss-Magnuson Act requires the dealer and/or manufacturer to prove the modifcation cause the problem, but MB can probably afford better legal representation than you or I.
The ASP puslley is a special order. You need to call them and talk to Lee. It takes about 4 weeks to get one.