Well, it looks like the big question, Catzen, is if you have Teleport, Create Portal and Call of Home spells? With these spells you can move quickly to and from Brimlock Roon. If you cast Create Portal near the exit of the Dragon Spire the first time through, all you have to do is enter the Spire the next time use the lever and then cast Teleport and "poof" you are at the exit. Or you can go back to the "areas" of Ishad Nah (as long as you don't go into town) and cast Call of Home to go back to Brimloch Roon - "poof" there you are!
As for experience, set your spawn to frequent and kill more monsters. Also, traveling in the water without a boat will give you more chances to kill things and increase experience. And then there is the bug that when you kill Grue Morges (uncertain spelling) for the Thieves Guild in Ishad Nah, every time your thief goes in there he will continue to give you experience over and over (I understand the patch fixes this bug). Or the one in Birmloch Roon Thieves Guild is finding the Leprecaun's lucky clover located in his treasure chest. I have the patch installed, but continue to get 5000 experience points every time my thief goes into the pawn shop.
I believe as long as you have money to buy training in a craft, you can continue to get spells with level ups. Although you may have to change your role again to something different, like a Ranger or Monk to begin getting spells with level ups again. And there are also "Spell Books" you will find to increase spells if your caster has achieved that particular level of the spell, all you have to do is "read" the book you found and acquire the spell.
I couldn't resist giving my two cents since you asked, and the forum has been down so I really needed to answer some request for help to appease my lack of forum syndrom again.
God speed to you and your party!
Mammawlin
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mammaw's know all, see all, tell nothing