Article that I agree with about how owning a camera is a very difficult business model:
Owning vs. Renting: Why I Never Bought a Camera at DV Info Net (http://www.dvinfo.net/article/pre_production/buyers_guides/owning-vs-renting-why-i-never-bought-a-camera.html)

Most audio equipment doesn't change much, so I've accumulated quite a bit of pro audio gear, despite the fact that I'm still starting out as a pro and haven't yet earned what my equipment is worth.

The one piece of equipment that would be next on my list is a better set of wireless like lectrosonics. Right now I'm fine renting them when it's called for, but frankly I just don't like the hassle of renting: negotiating it with the producer, scheduling the rental, checking everything over, picking it up, dropping it off. Most of the time I get better results if I use that time for dealing with wireless issues on set even with my g3, so usually I don't bother requesting the lectros.

It's clear that the analog wireless bands are going to be in flux as the digital transformation happens, so my biggest concern is that I purchase a set of lectros and the next day the government revokes those frequencies. Perhaps better just to buy a set that are already using illegal frequencies if those frequencies seem to work well locally, given that the cost can be a fraction of the new cost.

I have a basic kit of two G3's and hand held radio mics but for anything major I rent in pro radio mics.

The 600Mhz block is going up for auction next year. I would surmise those frequencies wouldn't actually be illegal until a year or more after that. Even then, out in the middle of no-where, I doubt the FCC dream police would come to get ya.
I own 6 G2/3 and 4 Lectros. If a client has the budget, I'll use the Lectros', otherwise the Sennheisers' .... the Lectros don't see all that much use, but they've paid for themselves in equipment fees. So it depends on your usual client base and payment structure. I mostly do production sound on films these days, so equipment is 'rented' to the client as a package or a la cart.

It's clear that the analog wireless bands are going to be in flux as the digital transformation happens, so my biggest concern is that I purchase a set of lectros and the next day the government revokes those frequencies.

Lectrosonics' on frequencies. (http://www.lectrosonics.com/FCC-Spectrum-Updates/fcc-a-spectrum-updates.html)

Perhaps better just to buy a set that are already using illegal frequencies if those frequencies seem to work well locally, given that the cost can be a fraction of the new cost.

NO. Do not do this. If you interfere with local safety communications (fire, ambulance, police, etc.) you could be endangering other people's lives. It's unethical and immoral to endanger other people to save yourself a few bucks. Don't do it.

On the flip side, RF activity in the frequency bands taken over aren't restricted to low power like we are. You'll be subject to large and unpredictable RF hits making your illegal radios just about unusable.