The GT series is a very reliable lawnmower that is easy to transport (fits in back of a full size truck) and simple to maintain/repair yourself- air cooled engine, no hydraulics, no power steering, easy to replace filters, etc. I'm accustomed to the larger 455 diesel we have, but all of our friends and neighbors still think our GT275 is a beast compared to their wimpy Murrays, Yard Machines, etc. The 23x10" rear wheels give it plenty of traction.
Have you seen the GT242 in person? In my opinion, $1500 with those attachments isn't bad if everything is in good condition. The lawnmower isn't very heavy, so I'm guessing the owner has weights attached somewhere (or is very obese) for the plow to be effective. You should have no problem mowing 2 acres, but I've heard the front snow blowers are a pita to install/remove. You might be better off scraping the snow off your 500' driveway with your blade.
We purchased the GT275 new in 1998. It's been a great lawnmower, but had it's fair share of small problems- it is very similar in specs to the 242 but with 3 more hp. There is no hour meter- which I've always thought is a very bad idea/poor design.
One thing to note, I'd say over 50% of all the GT series that I've seen from that era have a cracked hood, or at least one broken hinge on the hood. The hood design is a large single piece of plastic with the hinge integrated into the design, so you have to replace the entire lower hood for around $300 to fix a broken hinge. I normally wouldn't care that much about a cosmetic problem, but the hood on my GT275 fell off while mowing a hillside a couple years ago and tore apart the wiring harness for the headlights, so I currently have no headlights.
If you have the funding available, you would be getting a lot more tractor with the 445. The GT275 is a lawnmower; the 445 is essentially a compact utility tractor with turf tires and mid-mount deck- shaft driven PTO powers the deck. I'm guessing it will also retain its resale value better than the GT242. 500 hours is like new for one of those, and it cost about 10k new, so $4000 is a good price, regardless of its condition. However, it will cost more to maintain.