I happen to have a unique perspective on this at the time.
I've recently started introducing "scanning" to a few friends of mine. For me it's an obsession they have seen me cope with for years now. For them it's a new hobby that is sparking interest. Depending on what stage you are in (or plan on ending at) you might be okay with just the Pro-96.
I have had the pleasure of owning both the Pro-96 and now, the PSR-500. For my purposes I can't see how I did without the PSR-500 for so long. But, depending on your requirements a Pro-96 might be just fine.
I started listening to Austin about 9 months ago I guess. I live close enough that I created a Pro-96 vscanner for them. When I traveled there (once or twice a month), the Pro-96 would do just fine with a few considerations. You have to understand you aren't going to be able to program in everything and expect to hear everything. As hiegtx stated, it only has 150 talkgroups per bank (which in reality is a lot). But for ease of listening you wouldn't make a whole bank of AustinPD (at least I don't). I made a few banks of APD broken down by districts, and also had the corresponding street response talkgroups. So immediately I had knocked out 6 banks (I always have one federal bank, one state agencies bank and one Texas DPS bank, + 3 APD banks). So now filling the last 4 banks was no problem. I found that I was wasting a lot of the available space of the Pro-96. It is possible (but requires extensive knowledge of button sequences), but you can go break things up by sub-banks to turn certain groups on/off. But this seemed to be a lot of work. To figure out how to best organize the banks, it took me a few weeks of climbing to the top of a parking garage (here in San Marcos, the highest point I could find that I could pull in the A/TC TRS). After awhile I had it situated. It can be done, but all of the file would be devoted to the A/TC TRS and wouldn't have space for LCRA (which is nice if you plan on visiting any lake/waterway around Austin), much less trying to squeeze in RR, Gtown, Travis Cty, etc.
But, if you don't care to listen to anything but APD ( as one of my friends does), you can just program in those talkgroups (I still broke them down by district), close the bank, and it works just perfect. If you don't close the banks, the system is so expansive you would be listening to unprogrammed talkgroups all day long. Since my friend isn't too crazy into scanning yet, it serves him perfect. He gets to hear why the police are forming outside his bar, and knows where not to put his nose. He doesn't need anything but a Pro-96.
However, someone obsessed with scanning (as I am I guess), couldn't do without the PSR-500/Pro-106. It has enough space for everything, and with its layout, is easy enough to navigate to certain lists (of which there are 20- imagine 20 banks), and open up many different talkgroups. I still get to have it broken down by districts and have enough room to include all the A/TC TRS I want to listen to as well as an LCRA site, a federal list, a state agencies list, a Texas DPS list (which is the whole statewide plan mixed with the A/TC talkgroups of DPS), + I still have room for all the FRS/GMRS/MURS/ISR frequencies and the AAR channel plan. All in one vscanner. It's amazing (not to mention, what I consider to be two huge abilities- NAC decode, which can really help identify a federal agency; RadioID display- which can really help you figure out how a TRS is organized).
There's a little insight. If you never get the Pro-96, and go straight for the PSR-500/Pro-106 you wouldn't know what you missed- you'd just know that your new scanner is literally "the sh*t." If you do get the Pro-96 understand what we have explained. Having had both I couldn't go back to a 96.
