I had the same though process as you about a year ago and ended up trying what you suggested. While you can reverse sear on a Memphis, the risk of a big grease fire is very big unless you catch any drippings in a pan (which can limit your cooking capacity). If you just let the drippings flow as normal, a good amount of fat, grease sits on the drip tray and side walls at smoking temps, then liquifies when you raise the temp suddenly spreading 'fuel' all through the grill en mass.
I would say the more expensive grills are like comparing an everyday day with a luxury car. They are built better, have a few extra features, and look much nicer. A lot of them will last 2-3 times as long because they are stainless and/or heavier gauge steel. A lot will run hotter and recover quicker for better 'grilling'. With the double wall insulation I can cook a brisket overnight in an Iowa winter and only use about 20 lbs of pellets. If it's clean, I can grill steaks, burgers, chops instead of just smoking food. The design of the Memphis in particular, really keeps more ash away from the food and cooks much cleaner than my old Traegers and GMG ever did. However, better grilling is about the only function it does that creates end results that didn't taste the same as food from my old Traegers or GMG.
At this point though, I ended up buying another Traeger to have with the Memphis so I can best use the limitations of both when cooking and have had both going at the same time several times already. I might suggest that if you decide to get a higher end grill and can afford it, keep the GMG until you're certain you won't use it as well.