Eeek, the 520's are the Jackson Glacier boots ... they're fine for tiny, skinny people who are just starting out, but they don't have enoughs support for grownups or even big kids. Once you're past the first few intro levels of skating, you've outskated those boots. (Your instructor's correct: very few shops will move/replace blades on PVC-bottomed skates.) I haven't checked them out in a long time, but the blades used to be really flat with tiny toepicks; again, okay for a beginning skater, but not for someone who's beyond the basics.
I usually ask the questions listed below, so I've answered them for you. Please correct me if I'm wrong.
. Are you still growing?
I think the answer's "no."
. Are you tall or short?
Tall
. Are you of average/under-/over-weight?
Over
. What level do you skate at currently? (or, what skills are you learning now?)
USFSA Basic Skills / Adult 2
. Did the Jacksons fit well? (Assuming they were the right size and you were measured properly)
I would suggest Jackson Freestyle boots and a Coronation Ace/MK Professional blade. The boots won't need too much break in time because they have good support without being stiff. Since you've been without any support/resistance in the current skates, you'll be comfortable in these boots. If you're really overweight, the boots will break down sooner than a stiff boot, but they cost less up front. Assuming skating will help you lose weight, you'll need new boots within a year anyway since they'll feel too loose. Why spend a lot of money on boots that will be too big withiin a year? Better to start with a smaller investment with appropriate support than buy too-stiff boots that take longer to break in and will be oversized anyway? Save some money now and save up for a higher-level boot next year.
The blade is a little higher (and pricier) than you need right now, but with the change in the USFSA Adult curriculum coming up this season, you'll benefit from the all-purpose blade. Since you're not growing, next time you upgrade boots, the blades can be moved, so it will save you some money. (Clone of those blade models would be fine, too.)