I suggest skilling up on a mob. Also, if your blu magic skill is above eh 250 like you said, take off all the skill + gear you've got. I find that having all that gear on sort of confuses the skill up process. It has been stated by SE that the higher your skill is the more difficult it is to get skill ups. So when you put 15 or more skill lvls worth of gear on, the game reads your skill as 315 when it is really 300, so you will get skill ups as if your 315 (more slowly) then the 300 you really are. It's just an example, but i find it true with almost every skill i've ever tried to level. Also, as brd i went from 210 singing/wind skill to 259 singing/wind skill on the pink-fish/dolphin things in sea, using threnody, took about 30 mins. Then tried to skill up in port jueno on string skill while i waited for a party, using carols on myself, got .1 or so every 5 to 6 mins (15 or so casts).
For the enhancing magic problem, the best - only - way i have found to lvl it quickly is to get in beseiged and find a general that doesn't already have pro/shell 4-5 and spam pro/shell 1 on them over and over.