Again, apologies for the latency.
The following is strictly IMO, and others might have a slightly different take. The typical recommendation to stick with sub-liter bikes is geared more towards either sport bikes, or young riders. Not new riders, mind you, young riders. Absolutely, a 1000cc sport bike would have enough power to get you into trouble even if you're careful and attentive. An 1000+cc cruiser, though, only has enough power to get you into trouble if you're being irresponsible. You'd really have to work at it to let an 1100 get away from you. If you think you'll succumb to your baser urges, then maybe stick with a 750.
Again IMO, this gets less true somewhere between 1400 and 1600cc. At that size, even a low-key cruiser can throw you a loop if you get distracted.
On the other contenders you mentioned. Again, you can't go wrong with a Shadow. The ACE or the AERO are both great bikes and neither of them should be tough to maintain given a clean history. Look for signs that it's been down, and for a quick assessment of how well it's been cared for look for rust on the brake reservoir cap and in other seams or bolt heads.
On the Intruders, although I absolutely LOVE the look of them just as you said, I don't believe one from the 90's is going to meet your reliability requirement. I'd love for you to prove me wrong, and if you get a real good vibe from the buyer and the bike looks just immaculate, maybe take the chance.
For what it's worth, a quick scan of my local classifieds service isn't turning up a lot of great options at $2,000. It's been a pretty warm winter though so I don't think prices have taken a hit like they usually do. The best price for a 2005 Shadow VT1100 I'm seeing is $2,695. So your mileage may vary in your area.