1. Take a deep breath
2. Reset your expectations
3. Preferred Plus is not an open invitation to an upgrade
4. The Preferred programme basically allows you to bypass the counter (after your first rental) and earn more points
5. It's similar to Hertz Five Star ... "upgrades where available" ... far from a guarantee and not all (particularly franchise) locations participate or willingly give you a better car for nothing ... and the US>EU and EU>US doesn't always translate ...
6. Upgrades are invariably limited unto a certain level (i.e. full-size in the US) ... doesn't mean you won't let lucky and receive an SUV or a luxury
7. If you want a particular vehicle, rent it ... don't expect to upgrade into it ...