"Um, building train tracks? A grown man?
Is that really a very attractive trait in a partner?"
I think some of the less dorky hobbies are not as conducive to a happy marriage and family life as people might imagine. :)
I have had to give up a few of them since settling down, and whlie I couldn't do toy trains, as time goes on we do both develop more dorky interests. I build fairly pointless machines and have taken up a second academic career, DW crochets and crafts and sells what she makes - we can do our hobbies in solitude or alone and be truly happy, who cares how attractive it is? :)
I wouldn't be judgy about trains, either. Surely one of the pay-offs you hope for as you have to get old and gross and slave away for years is eventually, hopefully, being able to do little things you always wanted to do, but didn't have the money money/time/support to do. I know I have bought things as a dad that I have wanted since I was a teenager, things I might not even use that much but which create happiness because finally I can have the top-of-the-line version of that thing. DW has done the same.
@OP - congratulations to you and DH. I would go with it, there are few things in this world like being able to realise a life-long dream, however small, and few people lucky enough to see someone they love do it, let alone do it themselves. Are you going to do something similar?