The warranty difference is not a big deal (so they should give the longer warranty). Generally if there is going to be an issue, it will show up pretty early. The speed range is pretty narrow (bottom end is still too fast and the top end of only 1600 on a small machine, nice if it was faster). However that fast bottom end seems to be very common on new lathes - I suspect there is a cost saving, and with VFDs being so cheap, it is easy make the conversion and dial down another 50% (which would be about right).
I agree, if you know you are going to stay in this game a while - get the better machine (in fact, step up from the 1236T to at least the 1340GT). When you get a better quality machine, you'll use it more, enjoy it more and when you get more machines, it will always have a good place in the shop. It will also sell well when the time comes. I spend $10,000 on my first lathe - it was nearly new, I was 21 years old. I spend every dime, I could not even power the machine. The only tooling I had was a 6" caliper and a set of drill bits. I figured it would be the only machine I'd ever buy, so I'd better make it a good one. Over the years, tooling was added. That was 34 years ago. I now have several more machines, and the cost of all the others put together comes to what that first lathe cost. Obviously I way over paid for that first machine, but I've no regrets - that was a great purchase and it is still my "goto" machine. The original purchase price is long forgotten (I've blown more cash than that on any number of stupid purchases). For a life time machine, don't sweat the price!
A 13" machine, with a gap is a very useful size for general type work. If you have the space, power and ability to move it - then anything up to 16" would be an excellent choice (still very capable of small work). IMO over 16" gets to be a bear if you are mostly doing small stuff (of course it would still work, just not as handy, everything is bigger and more expensive).