I personally would avoid group travel to continental Europe, and would not really read much into rates they charge one way or another.

For what you are looking for consider doing it yourself and just get organized and send an itinerary to your travel companions, perhaps with a virtuoso agent helping you if you have luxury bookings, and thru those hotels you can have excursions, transfers arranged easily enough. If you work with one agent, and stay in all lux properties you'll probably get a lot of help putting it all together from a reputable agent. If you just want some virtuoso level properties for amenities and a few more budget friendly hotels thrown in you'll probably have to do more of the groundwork yourself.

i had considered hiring someone to put together a self driving trip to Sicily a couple years ago when i was quite busy at work, similar to what you are looking for, but quickly changed my mind. I actually enjoy the planning process myself and managed to find the time. The agency i had communicated briefly with has a Spanish branch: Spain | Authentic Explorations (authentic-explorations.com) . If you are looking to spend >$1000/day pp but don't necessarily need a over the top hotel this type of customization may work, as they will likely be fee based. Whereas an overseas agent probably would get the bulk of their remuneration from hotel commission so harder to justify for what your describing. i simply found them from some Conde Nast/Travel and Leisure recommended list so can't really say much about cost/value/experience. If you do something like this on a luxury level be sure to report back.