Running shoe advice

it sounds like what you're benefiting from is the cushion.  Triumphs are well cushioned shoes- so, not a bad choice, but there might be some newer high tech designs where the cushion lasts longer.  I had good luck with nike Lunarglides lasting 500-600mi for me.  Not sure how the Adidas Boost line is- but probably good?  You may want to ask the folks at your running shop about which shoes they find hold their cushion the longest.  Sadly- shoes do wear out, and each person wears them out differently.  

The Triumph 10's are now last years' model, so perhaps you can find them on sale and buy 3 pair.  ??

Or- you could go with the more highly cushioned shoes.  Like some Hoka's or altras?  But more cushion often results in less stability.  comfort first.

and - like you said.  strength training, cross training, cycling- may all be in your future.  

I try to get 500 miles out of each of mine as a matter of principle, but often that final 150 miles I'm pushing the injury envelope.  So, one trick is to interleave new shoes with old shoes.  You can squeeze more miles out of the older shoes- if you don't run in them every day.  make sure you buy them in different colors and log the mileage separately, so you can tell them apart.

My local shop takes used shoes in to donate them.  That might make you feel a little better.  There's a high school kid somewhere who cannot afford $120, that would love a pair of gently used 200mi Triumphs to run in.