The maximum I managed to get on my hybrid Thief was 504. Gonna post a screenshot as soon as I find my saved game.
There's actually a bug that gives you a 4 point bonus for getting Detect Magic from the Meeps. This is the VGA version though, so I'm not sure about the EGA one.
Also about the topic, I always tend to build a Thief hybrid and max every skill in every game except for Quest for Glory 3, because there are a lot of skills that I am unable to cover. The only things I didn't manage to get throughout all four games as a hybrid Thief are:
- A Broadsword and a Shield in any of the games except for QFG5
- The Juggling Lights Spell in QFG3
- The Lightning Ball Spell in QFG3
- The Summon Magic Staff Spell (if that's how it was called) in QFG3
- The Ritual of Release Spell in QFG4
- The Resistance Spell in QFG4
- The Dragon Fire/Healing Spell in QFG5
Everything else is obtainable in my opinion, disregarding the Paladin spells/points obviously. Also, I was unable to max climbing in Quest for Glory 2 without abusing the magic rope (which the game does not allow).
An optimal way of getting the Lightning Ball and Juggling Lights spells on an imported character is actually rerolling your Thief to a Wizard when you hit QFG3, since Thieves get no love in Tarna anyway. You get to keep that spell, but the Summon Magic Staff one dissapears as soon as you import into QFG4 sadly.
I am not quite sure if you get both of them regardless of how you did in QFG3 provided you have Magic learned... But they are learnable in QFG5 anyway, so yeah.