Biggest reason to get your own skates? Pretty much everyone's alluded to it without directly coming out and saying it. Skating is a kinesthetic sport - to get good, you need to know how the elements "feel" when you do them correctly. If you have improper equipment, you won't develop that kinesthetic awareness.
I've been skating for five years now, and spent the first three or so trying out three separate pairs of skates before settling on my fourth pair, which fit properly. I've been wearing those for the past two years, and have already replaced the blades in the last six months--but I skate A LOT. Between better equipment and my back surgery, my skating has improved dramatically in those most recent two years.
Examples:
1. The first five times I tested my bronze moves (prior to 3/2008, when I finally passed it), I was skating on boots that had no support and blades without rockers...and I thought it was JUST ME and that my 3-turn technique must be uber flawed if I scrape that much. And, I could not spin for more than three revs to save my life.
2. The next time I took that moves test, I took them in boots and blades similar to what I have now (Harlick high test, my latest have an oversized toe box, MK parabolic blades), but they were a width size too narrow. I had way better edge control in them and I passed the test, but I developed bone spurs on my pinkie toes and the toes next to them. And spinning was still a challenge.
3. When I finally got skates that fit me, I could definitely start to feel my edges even more, was able to better feel where I was balanced on the blade, got my forward and backward 3s clean, and low and behold, I can now spin and maintain more than a few revs.
Equipment matters.