In the locations I frequent...
Most of the National locations I go to (outside of New York) have a very big difference between the Emerald and Exec. Aisles. For my last 10 rentals or so, I have driven Avalons and Volvos S60 mostly- even saw a Cadillac STS at the MCO Exec. Aisle but I needed a Minivan that day (weren't any Minivans in the Emerald Aisle) so I missed out on that. I almost never see these premium cars in the Emerald Aisle- and I check (just b/c you never know- there may be something better in the Emerald Aisle- hasn't happened yet). Question is- isthat important to you? If you're very happy getting your Grand Prixs and such probably worth it to lay out the money (also the rental credits- depending on how much you rent next year may be worth it). If sometimes you're gonna need Minivans (not to say there aren't Minivans in the Emerald Aisle- it's just not as frequent) or like to have bigger cars and leather seats and more power (love the Volvo S60)- then it's definitely worth it.