The misinformation being spewed in this thread
I will do what I can to sort through it and present you
@Wally Russell with the tried, true, and PROVEN FACTS ONLY. Nothing I tell you is heresay, based on my single and limited experience, nor a matter of opinion. All information and suggestions that I offer will be things that are factually grounded.
Firstly, these two sites need to quickly become your best friends, I have accounts on both. Crownvic.net (awesome forum) and ADTR.net (awesome for parts/upgrades). Register now.
Now, on to the fun part..
It's a 4,000lb car that gets 16 mpg city and 21 hwy with a V8 engine. And that's just on Vics with single exhaust.
OP's Vic is probably dual as well, and will actually average closer to 16city and 22hwy, since almost 500lbs+ of police equipment will have been removed by the time you get the car, making it lighter and easier on the gas.
SOME departments do in fact have kevlar (ballistic door panels) installed in their P71s. Maybe not in your department, but you are wrong to say there is 'zero'.
Side note though, even the depts without the ballistic door panels will generally still have a type of kevlar liner without the ballistic properties installed, designed to protect against sharp objects in the trunk that may penetrate into the fuel tank on high energy rear impacts.(im sure you're familiar with that whole recall).
Complete and utter horse sh!t.
And that's before mods. And I'm talking cheap, easy mods that anyone can YouTube and do to their own Crown Vic and turn it to a very fuel efficient vehicle.
I could be wrong since I don't have a picture to go off of, but, what it actually sounds like you have going on is actually a common problem with many Vics, and that is excessive brake dust. And switching from stock wheels to rims will not help you at all, it'll only piss you off because then it'd be your rims getting filthy every 2 weeks. With our cars you're just going to have to wipe your wheels off more often than usual(if it's the brake dust issue), or, you can buy these babies for about $150.00 and, not only look cool because of the colors, but you'll also stay cleaner, longer, too

(and im sure if you wanted to go cheaper then you can find brake dust covers for cheaper on amazon, i just chose these as an example)
The only high mileage car that I would ever put my money on would be a police interceptor. These vehicles routinely make it to 300,000 miles (mostly the fleet ones because of how often they get used and recycled). But, you make a good point to just simply stay away from those if you can. There are plenty of government fleet Vics, fire chief's Vics, high ranking law enforcement ppl's Vics, floating around looking spic and span brand new with under 100,000 miles to just jump right into a high mileage one.
But who knows how much $ OP was working with?

$1200 for an 09 that will probably not need much and easily run another 175-200,000 miles if cared for properly, isn't that bad at all

I can understand how putting more into the car than what you paid for it can seem a little

at first.
But with the Vic, once something finally does eventually break, it's usually always easy to fix, and generally never has to be fixed again after that(if done right, and done with quality parts).