Go for TK Comfort.
I found the seat to be quite a step up from UA E+; the comparisons to UA's domestic F seats are correct. No foot rest and the pitch and width aren't quite as great, but still head and shoulders above any economy seat.
I also thought the food was excellent - for airline food. I was able to compare it to TK's C class food, and it's almost as good. Loads and loads better than UA's Y catering.
A $100 premium (+lost bonus miles) is well, well worth it. What wouldn't be worth it is taking a longer route (significantly more hours of flying) just to have Comfort instead of, say, a non-stop in regular Y. For instance, I wouldn't fly from North America to IST on my way to western Europe just to be in Comfort. But with BOM-YYZ, stopping in IST is still a pretty direct route, so by all means do it.