I not only run the DragonQuest system to this day, but I'm writing a new campaign for it. I have a home-brew rulesbook that essentially takes all the stuff from the revered SPI 2nd Edition and combines it with the new elements from TSR's 3rd edition. And since 2 + 3 = 5, I called it 5th Edition. For the capsule adventure in the back, I adapted the original WFRP adventure "The Oldenhaller Contract" for the DQ rules. I even use the same 3-column format, the original fonts (including
Thaelia), and matched that pinkish-mauve color used in the tables. The only real deviation is that I added color illustrations, but still included the original art from DQ 2nd (where I could find it).
As to Colleges of Magic, it depends on the goal of the character-adept. If you want to go the path of utter destruction, then the College of Fire Magics is a decent fit. But say you wanted a kind of fighter-adept, where most of your combat came from your preferred weapon, and your magic simply supplied some handy spells. In that case, Ensorcelments and Enchantments seems best. "O Great Crystal of Vision..." Without doubt, the most expensive college in terms of just about everything - time, Experience Points, monetary expenditure, and even the sacrifice of some very expensive Endurance - would have to be Shaping Magics, but if your perseverance is up to snuff, you can churn out some really interesting and very useful items.
Oh, and to Thomas Shey's point, I left out my 5th Edition most of 3rd Edition's nerfed rules, using the 2nd Edition as my primary base. Because I included a full TOC and index, I ballooned the number of pages from 156 to 298.