So I own some glocks. They're all 9mm's except for one that I just got from the EE here. It is a 10mm, glock 20. I got it to replace my 357 mag as a woods gun. I knew ammo was expensive when I made the deal, but I am put off by spending 50 cents a round to blast at the range. I am contemplating putting a couple hundred rounds through the 10mm to establish reliability and familiarity, and than doing the majority of my training with the 9mm but still shooting some 10mm each range session to keep things fresh. In my mind, it stands to reason that shooting one full size glock would help me improve shooting another glock of similar size. Kind of like when people shoot 38 to cheaply practice their 357. I know the recoil is significantly more than 9mm but then again, 357 kicks the crap out of 38 and that's a pretty accepted practice technique. What do you guys think?

I have no issue with it. It's one of the strongest cases for the Glock family of sidearms.

Tried and true method. Many shooters use 22's to reinforce the fundamentals.

One option is to shoot a mag or so through the big boy every trip or every other trip. You keep your familiarization and don't waste a ton on ammo. Reloading drops the cost significantly on this round.

I think that's what I'll go with. I'll probably shoot it a little each trip to keep it fresh in my memory and every once in a while dedicate a range trip to it.

I don't know if you reload 40 but it will run just fine in a 10mm Glock with no changes.

If you reload 40S&W why would you not simply reload 10mm.  The same dies and components can be used to reload either.

40S&W will work in a 10mm but you are head spacing off the extractor rather than the case mouth. YMMV