No, Grandpa, you aren't alone. Almost, though. I too like to build diverse subjects, but I get the impression we are in the minority around here. To a lot of people switching from armor to aircraft or vice versa feels like cross-dressing.
Let's see, I started the year by building a Benetton 188 and a Dodge Viper. Then I moved on to a 1/48 A6M2 and a Corsair (they got into a fight when I set the boxes next to each other). I dropped those to do a group build A-36 (which is what I should be doing instead of fooling around the computer). My next project will likely be an M1A1 Abrams or a Sherman M4A3. Other than race cars, muscle cars, prop planes, jets, armor, and the odd figure, I don't have many other interests.
I guess that leaves out ships and sci fi, but I wouldn't count out doing a ship sometime. I do have one in the stash somewhere.
Building across the board makes you a jack of all trades but a master of none. No matter how good my Panzer Mk.VIb ZR-1 looks, I'll never enter it in a contest because I know someone who lives for that subject will discover I used the wrong shade of gray or forgot to correct the JRS pod by adding a bump on the fender. That's OK, because it is a hobby, and I do tip my hat to those who love a subject well enough to get a PhD in tankology or resin chemistry.
I really like things that go fast, shoot straight, and fly high, so I doubt I'll ever be able to settle down to one genre, much less one subgenre, though I really admire the work of those who do. For me life is exciting all over the place. Everytime I go to an airshow I can't wait to build an airplane and everytime I go to a race I want to build a car. Maybe I'm just too impressionable.