No, I think you misinterpret what some people, me anyway, mean in talking about vehicle size. For me it's more about proportion and what shape and volume of interior space do I get for the external footprint. Many of these smaller vehicles are kind of crap in terms of interior space to exterior footprint ratio with all their tapered roof-lines and sloped sides with bulging fenders.
Also, not everyone is talking about kids when they want interior space. These smaller crossovers require hauling cargo boxes on the roof in order to bring much along. Some people ski, mtn bike, etc and don't like to put these things out in the open on a vehicle in the elements, etc. Additionally, a small fuel efficient vehicle usually sucks with massive cargo boxes or bikes on top killing the fuel economy and handling in the process.
This is my break down I have three vehicles in our fleet its been that way since 2004. That and I have a fourth option in the driveway nearly every day.
2010 OB replaced a 2001 Legacy the daily family Mule and road trip machine
2007 Sequoia the bus replaced the 93 Land Cruiser driven daily by grandpa the kid shuttle operator
2001 jetta 1.8t wifes first car the beater rarely ever has more than one person in it.
Grandpas ride left at the house daily while hes the kid shuttle bus in the sequoia. 2005 SLK 350 17,150 miles on it as of this morning.
I use the beater vw for solo trips on the weekend tight parking being a big reason I like taking it.
My interest in the GLK250 BLUTECH is a replacement for the small vw. That and I've had lots of sucess finding low mileage premium brand vehicles the past few yrs at big discounts!!! I would rather have a low mileage single owner richie rich GLK for 20k than a beat to crap VW or Subaru for 20k ;-) So i see potential for tge GLK to be a good value if compact and rear seat space is not a deal breaker.
My rule for Subarus buy new be happy. Buy used, you end up with a very very very used Subaru with a high used car price. Not my idea of a good value.
The Sequoia is nice but given the choice Ill opt for the smaller car choice every time. Hell if I can fit my gear in the SLK 350 he'll yes its the SLK I'm going with. If I still had motorcycle privledges Id take the bike. Kids canceled my motorcycle fun.
Off pavement capability I would put the US spec GLK about even with the current cvt OB with xmode, they both more or less have the same limitations on soft low hanging fruit regarding hitting something hard on the trail. The 7spd system and engine in the GLK being better power and cooling than the cvt subaru. Not counting Space!!! Of course.