Hmm, I'll definitely make the characters you mentioned a bit tougher. I think there may be too many monsters on the bridge and the prison. If I lower the amount, I'll have to increase the difficulty level or the respawn rate. 1.5 is pretty big, but I'm sure it will be a worthwhile victory to pursue if I tighten some of the loose screws.
I must also remember to tone down the old Dragon Cuirass... maybe they should be made of stone materials.
Yeah, basically you should make the forest increase in difficulty each level, but reduce amount of monsters spawning on some levels.
The only reason I can't do the forest untill GC3 is because of the eagle around forest level 4. Its good for keeping people from an early win, but once you've gotten to GC 4, you're ready to do the whole forest, which is kinda too easy in my opinion for a win. Also, its very easy to avoid mobs when there is no specific path(bridge over river, prison exit). If I'm really in trouble, I just leave the forest, you should maybe add some kind of wall along the edges except for the beginning entrance at deep forest 1 near the west side.
Also, I recall seeing kobold casters once or twice, but they're really weak. A suggestion would be to make them on par with mystic dark frogs and have them be a higher frequency mob spawn in deep forest, to add some difficulty. Or am I wrong about them being low difficulty monsters? I never see them outside UT.
Edit: I also think the goblin jailers should get upgrades too, but have them spaced out throughout the prison, like 2 guarding a door, 4 in the room you enter by sewer into, 1 for each prison cell, 2 "elite" guards with the head prison goblin, etc etc.
Maybe add many houses outside the prison that were raided and turned into goblin barracks filled with the upgraded goblins or maybe some of the already existing ones? I don't know how hard it would be to code this, but if possible, it would allow you to turn off regular mob spawning.
They'd all have to be guaranteed to see you before you leave though, or it would be too easy to avoid them.
I've only seen dragon cuirass in shops and gotten it by wishes, but I find the golden jaguar shirt to be a much better choice.
These are only opinions and suggestions though, do what you see fit. I'm enjoying CLIVAN a lot.