Biggest regret....selling my collection in my early 30s to fund my own startup business. Even that is not so much a regret, since the business did operate for over 5 years before finally closing down (opened online DJ store, by 2008 no one was buying hard copy new music and my wholesale suppliers had gone into bankruptcy, cutting off my supply. Choice was either wrap up business or increase prices by about 2x to cover cost of directly importing product from Europe. Made the sane decision to wrap up.) But by my early-30s I had a really well-developed, mostly mint WW collection strong in Europe and Middle East.
Having said that, now that I've come back to active collecting I am having a lot of fun basically starting over from scratch in those areas that I didn't
inherit collections from when my father passed away, and building upon the collections which I did
inherit from him (USA, Canada, Australia, New Zealand, Malaysia-Singapore).