Hmm. This is an interesting question. I don't get much time to practice anything other than dance patterns, so there are many things I haven't tried. And most of my experience is things I used to be able to do, but now can't. But with no time to practice them, I obviously can't improve.
Spread eagles and bowers, could do them as a kid, can't now. Ticks me off. I also have crappy turnout, and "faked" them as a kid- i.e turning out more with the knees to compensate for the hips' inability. So I am a bit worried about blowing out a knee or two doing these, but that's never really stopped me before. I do stretch them every session though, hoping to improve that turnout.
Back spins. Same as above. Ticks me off, too.
Ooh- this will fit your bill- various front catch-foot positions (in French these are called Y- where you hold the foot out to the side with the same-side hand and F, where you hold a foot in front of you with the opposite hand, there's probably a name for holding the foot out in front with the same-side hand, too but I missed it). My 15 year old body would have been OK with these, but my 41 year old body had something to say after our coach had us doing these on a pre-gala "play" session.
Lifts and partner spins. Loved partner spins as a kid. When we have the "play" sessions to start igniting inspiration for end-of-year Gala routines, the coaches last year had us doing these. I can not do partnered spins anymore, although we didn't actually try the one we used to do most when I was young. Lifts....I am not a couples skater. That is all.
While I liked patch as a kid, I would have found doing lots of edgework on freestyle slow and boring. Now I do like that, and could and sometimes do, spend an entire session on various edge exercises.
And finally- physical training. I would have loathed and detested any off-ice training (other than jump practice) when I was young. Weights? Blech, Running/intervals? No thanks. Planks/wall chairs? Run away. Now, I like it almost as much as I like actually skating.