I've currently own an ST4s and have ridden a friend's ST2 many times. You won't miss the power of the 4 until you get into some fast sweepers, somewhere you can use the revs. The ST2 has more below 4K, they seem pretty similar to about 6.5K, and then the 4 takes off. For touring the bikes are ergonomically identical (at least until the recent update of the 4s), and there are lot's of aftermarket accessories available. Along with the other recomendations here, try Dr. Desmo for peg lower and bar raising kits. Sargeant saddles are available cheap. Of course if you're buying new you're getting an ST3.
The lack of reliability reports here are overstated in my experience, no problems in 15K miles for my 4s, my buddies 2 has 27K and no problems. Service will be more for the 4, but you should learn to do it yourself.
The lack of reliability reports here are overstated in my experience, no problems in 15K miles for my 4s, my buddies 2 has 27K and no problems. Service will be more for the 4, but you should learn to do it yourself.