Don't get emotionally committed to purchase ANY airplane until after the results of the independent mechanic's pre-buy inspection are in. Deal breakers might include significant corrosion and uncertain, potentially "service limits" provenance on the last engine overhaul.
Regarding density altitude ("DA"), no non-turboed airplane will climb really well above 12,000 ft but the Dakota and Skylane (~230 hp) will do better than the 160/180 hp passel of aircraft. Also, the Cherokee 140/Warrior models are notorious for poor climb above DA=10,0000 ft. If DA is a big concern for you, pay up for the Archer or buy a Cessna 172XP. BTW, I fly a C-172 with the O-320 D2J engine and Powerflow exhaust, probably about 175 hp. I am fine in the mountains, even on hot days, provided it is just me and maybe one passenger. Message: you can manage DA better with a light load in passengers and/or perhaps fuel.
About ownership in general: I think it is the only way to go if you fly >100 hr/year and can afford it. I absolutely love the freedom to fly throughout the West, over/around mountains, maybe to Mexico once in awhile; all without dealing with any FBO's annoying but perfectly understandable requirements (> 1500 hrs here), and of course the aircraft is nicely appointed and always available to me. I understand it may cost me more than driving (but not as much as spur-of-the-moment airline ticketing, even for one). BTW, I bought my airplane nine years ago with the thought I'd mostly be doing local hamburger runs. Instead, I've ended up flying it all over the West, over/around mountains, to Mexico, and coast-to-coast. I travel at a glorious 108 kt but I spent the money for an autopilot and a comfortable interior. A little extra speed is less important than you might think but range and comfort are both under-rated. I fly from the SF Bay Area to Tucson faster than I can get there door-to-door flying commercial (like with many flights, there is no nonstop service available), for example.
Enjoy,
Don