Justice,
Here's the perspective of but one "low end" guy.
Yes, it is possible to rent everything, all the time. The tricky part, as you probably know, is finding clients willing to foot the bill for the rental AND your labor.
The only times I remember making out well with a 100% rented system were special occasion one-offs, like New Year's Eve. I just don't think I would want to go through the process of renting entire systems on a regular basis, however, for a couple of reasons.
Availability: Small rental companies only have so much gear, and do you want to have to call them first, every time, before you say "yes" to a client?
Time: People are always calling at the last minute, and this goes back to the availability factor. You should really call at least a few days in advance if you want to rent an entire system.
Quality: Small rental companies, in my experience, don't have the kind of gear that I would want to base my reputation on. Especially if I was relying on them 365 days a year. I've held my breath many a time hoping that the old, beat up amp that I had no choice but to rent would make it through the gig. The stress multiplies with each rented component. I should add that I spit polish my own gear and sing it lullabies every night.
As a small time sound provider, renting should have one place in my world: to pinch hit for inoperable gear.
If I could give you one more piece of advice it would be to at least hang on to your cables, mic cables in particular. Its just a hunch I have.
Perhaps your options are more numerous than mine, but around here the rental gear available to the little guy is a bit dubious.
-Matt
P.S. If you haven't already done this, start introducing yourself to the folks who rent SR gear in your area. Get a copy of their inventory, familiarize yourself with it, and keep it handy.