I suppose I should chime in here since I trained up a a core of guys then ran them into their mid-late 30's.
Career Extension trainers are worth it. You can go through the both years of 33 and 34 with say 1-4 skill drops total, but 2-3 would be the most common by far. 35 is when some of the magic of Career Extension wears off and the drops hit harder. You'll start seeing some double drops, which is a skill dropping from, say, Prodigious to Wondrous.
If you've trained up a player (or bought him), and he fits your team exactly how you want. He's probably worth more to you than he would be on the Transfer List.
However, now is a very good time to sell 33+ year olds.
it will be interesting to see what the market thinks of those players.
The market for older players is temporarily inflated. This should be the last season of a mass of people promoting to higher tiers in Utopia.
16 new Utopia teams needing D1 payrolls. 40 new Utopian D2 teams. I'm not even going to count how many D3 teams would be really interested in 33+ year old players making between 10-40k.