I think if it's been working for you so far stick with it. My thoughts are if you in fact wanna upgrade that you pick a better fixture. There have been reports of these units catching fire, some say that was awhile ago some still stay away from them. They aren't even UL listed electronics.
If youre hanging the unit you might wanna hang a tad higher so you get more spread.
You also could go with LEDS too, a 30" fixture wouldnt be too crazy expensive I wouldnt think. And of course, you can always easily go to a top end T5 setup that would pretty much allow you to grow SPS
and whatever else you want, with the right bulbs of course.
The 30" tank is an issue as most people dont make one, they go 24" to 36" to 48". Here's a fixture I really like.
Current USA 30" Sundial T-5 Fixture 4x24W + LED - AquaCave
I also just did a search through my favorite sites and couldnt come up with a 30" MH
fixture. :-( It's such an odd size, I had trouble finding one myself.