32' to 42' in one day... that may be a record and congrats on figuring it out that you need a real MH.:B I made the mistake of starting at 36' because of posts on here that was the max for NP, SP, USFS,.... CGs. Learned that was not true so went 40 single slide and then when we could use over 100 days/year went to 42 and four slides.
Mine's 11 years old and I see no reason why it will not go another 10-15. I'll probably age out before it does. It would help if you posted the year but it sounds like a 2003-4. The old TV's are a blessing as now you can go with LED's which are very energy efficient and very thin so you can mount of the face of the cabinets.
I would not worry about the air systems other than changing the air dryer filter... the main reason the air systems do not give problems. I'll get a spare air bag this year as I have eight smaller than normal ones. I would agree that the Cat engine is good, but only if it's a 03 or OLDER... a 04 could have a 03 engine. If it's newer then do a google search on 'Cat acert engine lawsuits'. IF Acert is on the valve cover... run as they are dogs that only get 4-5 MPG at 65 MPH and give problems.
As for a money pit... Try $250K for a slightly used 04 that's now worth $100K and in another 10 years will probably be worth $40K. Has the $15K/year depreciation hit been worth it... HECK YES, and $6K/year for the next ten will be even nicer as half timers. :B
Ten years ago I was not educated enough to know you want Aqua Hot, Girrard awnings and a home refrigerator. In the last two day we've had two NoCold 1200 fires (running on electric) here in WPB. One burned through the roof before it could be put out and the latest only smoked the unit and blistered the gel coat at 11PM only because a neighbor saw it start. Even though I have a Amish cooling unit in mine I'm going to replace before going West this summer. Instead of taking the windshield out, I'll take a side window out.
Good Luck and it's a buyer's market so take your time... especially going for 32' to 42' in one day but your are on the right track. I'm biased towards the big Monaco's as I've had good luck with mine. I like their handling and if needed their customer service is very good.