Many years ago I put in a Stec-30 with altitude hold into my Comanche 250. Later on when I redid my panel and put in a Garmin 480 GPS I had it coupled with GPSS. In the approximately 10 years I,ve own the Stec-30 I,ve had one problem with it. When we redid the panel we shipped it back to Mineral Wells and have not had a problem since. Like Scott I do a fair amount of cross country flying. I love the ability to program my GPS, get airborne and hook the nav portion up and let the GPS and autopilot do the work. Once I get to the desired altitude I hit alt hold and then I sit back and enjoy the ride. Leaves me less fatigued and gives me much better access to scan instruments, monitor and switch fuel tanks, scan charts, eat lunch, or just admire the view.
I remember when I was deciding which Stec to go with the 30 or the 55. My initial thought was to go with the 55 and have the control head placed down around near the flap guage due to my panel location. When my autopilot guy said there are cables down in that area I said just cut them and get them out of the way. Little did I realize he meant control cables. OOpps. So the logical choice was to go with the 30 unit. This replaces the turn and bank indicator. As for the lack of ability to swap the Stec into another airplane, I've never really thought about that. If I bought another airplane I don't think I'd go through the hassel of removing my Stec and leave my Comanche with a coule of gapping holes in it to try to sale. If the airplane gets crunched totally then insurance just bought the plane and they can do with whatever. Me I'll go take the check and go get another plane. Believe me if you plan on keeping your plane for 10 years like you say you will, then you'll be glad you made the investment. Good luck.
Alan