I like to get at least one of each vehicle to open, if not more for army-building purposes. Even if it's not to scale (heck, what really is in most toy lines anyway) it's still enjoyable for me. I'd say here's what I have on display for vehicles, all in dioramas -
Diorama 1 - Dagobah w/ TRU Luke's X-Wing
Diorama 2 - Geonosis hangar w/ a couple Dooku Swoops
Diorama 3 - Jabba's Palace, no vehicles here
Diorama 4 - Purchase of the Droids, w/ the OTC Sandcrawler
Diorama 5 - Imperial Fortress (by Owen D) w/ 4 AT-RT's and one custom Landspeeder
Diorama 6 - Yavin Hangar w/ one large X-Wing, one Y-Wing, one custom War Speeder, one custom Troop Transport, one Millenium Falcon
Diorama 7 - Endor Battle w/ 4 AT-ST's
Diorama 8 - Mos Eisley w/ SAGA Luke's Landspeeder, one custom landspeeder, one custom ATL Interceptor, several Dewbacks/Rontos
Diorama 9 - Tantive IV, no vehicles
Diorama 10 - Tusken Slaughter w/ Anakin's Swoop and four Banthas
Diorama 11 - Yavin War Room, no vehicles
Diorama 12 - Dex Diner, no vehicles
Diorama 13 - Naboo Hangar w/ one Naboo Starfighter
Diorama 14 - Echo Base w/ one Snowspeeder, one Side Gunner and one custom Troop Transport
Diorama 15 - Geonosis Battle w/ one Hailfire Droid, one Gunship, one custom Homing Spider Droid (by Owen D)
Diorama 16 - Mygeeto Invasion, no vehicles
Diorama 17 - Outlander Club, no vehicles
Diorama 18 - Battle of Hoth, three AT-AT's and two Snowspeeders
Diorama 19 - Jedi Council, no vehicles
Diorama 20 - Courscant Landing Strip with Royal Starship
Diorama 21 - Cantina, no vehicles
Diorama 22 - Kamino, one custom Aiwha (by Owen D)
Diorama 23 - Star Destoyer Diorama (by Owen D), w/ two custom INT-4 vehicles
Diorama 24 - Boonta Eve, Anakin and Sebulba's Podracers
Diorama 25 - ROTJ Rebel Hangar with two A-Wings, OTC Y-Wing, Red Leader X-Wing, Milennium Falcon
Diorama 26 - Kashyyyk Battle w/ one AAT Tank, two mini Spider Droids, one Wookiee Flyer, two Crab Droids
Diorama 27 - Geonosis Arena - no vehicles but lots of beasts
Diorama 28 - Cloud City w/ vintage Cloud Car
Diorama 29 - Naboo Battle w/ two Fambaas, two AAT Tanks
Diorama 30 - Ben's home, no vehicles
Diorama 31 - Republic Hangar with ARC-170
Diorama 32 - Mustafar, no vehilces
Diorama 33 - Utapua with ROTS Gunship, Crab Droid
Diorama 34 - Death Star with Imperial Shuttle
Diorama 35 - Senate Duel, no vehicles
Diorama 36 - Dooku's Death, no vehicles
Then I do have about 10 or so extra vehicles that are kind of out of place on shelves or hanging from the ceiling.