The seaplane thing is definitely on my list, and I would love to do more aerobatics. And if I had the dough and the time, I'd love to get my multi just so I could get checked out in a DC-3.
I've been pretty lucky when it comes to trying out new things: won 1/2 hr of aerobatics dual in a raffle, got to fly two C140 (one on skis!) just because of my interest in the type (and got some citabria time as an offshoot of that), and my tailwheel add-on in a Champ was made possible only by winding up in the right place for a few weeks.
I've found that even a little taste of something new and different is very good for you, and I never feel bad about spending a little time and money on things like that instead of investing it in the usual thing. Had a lot of fun and learned a lot flying a J3, WACO, and the Ford Tri-Motor.
Right now, the "serious fun" goal for me is the PP-glider... amazing how much fun and skill-enhancing I got last season for so little money!! My season is delayed this year as we work on the 2-33, but that delay has allowed me to rack up a lot of time learning about aircraft maintenance (those certs are also on my "someday" list, and this resto will count towards that).
And of course, the upside to being "stuck" at the home 'drome all day when the glider club is flying is that I am more likely to be there when one of the guys is looking for company for a little hop in something else. That's how I got my insignificant but very enjoyable stick time in the RV-4, Breezy, Aeronca L3, and Grumman Tiger, as well as the local Champ. Might even get up in the Citabria towplane this season (didn't quite work out last year).
Anyway, I advise those of you who are on a narrow track, but often think of taking a detour, to just go for it! Sample stuff, put yourselves in new situations. It's good for you.