Full Time contract to fully developed players?

I know with a Full Time contract a player trains more etc, but I was wondering if "upgrading" to such contract is useful or necessary for players who have already peaked?

I mean, if I have plenty of players who, according to my AssMan, have reached their full potential or are close to that point, is it worth "wasting" money on them?

And in case I would keep them on a Part Time contract, is it going to affect their morale once I start to sign new players on Full Time contracts (ie. jealousy about higher wages)?

It depends.

Full-time training can help slow the decline of an older player, so if you intend to keep him in your first team squad for 2 or 3 years, it would be better to give him a full-time contract.

If you intend to release him at the end of the season, or he's back up, maybe no need.

Re. the last point - I don't think they get jealous, no.