Personally I find the off peak day return uplift from standard to first (£23.30 vs £16.80, i.e. £6.50) not unreasonable, especially with a railcard. The seats are wider and I find them more comfortable. Obviously though the optimum is to time it to the twice daily XC service!
Sometimes there is a drinks trolley too.
I do however find it disappointing that ScotRail only has one first class lounge, and that is in neither Glasgow nor Edinburgh.