I agree with others, do not fly Delta....I repeat do not fly Delta. I have flown Vegas to New York with Delta and New York to San Francisco, San Francisco to San Diego with Virgin America and would never fly Delta again until they make some changes. The Virgin Planes were new and have the cabin trim that we are converting to here. The staff were friendly and helpful compared to the obviously union tied Delta.
The Delta staff you refer to as "obviously union tied" are in fact non-unionised, except for the pilots.
I flew five sectors in Delta first class in December. I've also flown AA (mostly first class, but some coach), Virgin America and JetBlue recently, which is the basis of the comparisons I'm making.
While I agree that the Virgin America planes are newer (generally) and have a flashier cabin, my experience of Delta was fine. I found the cabin crew were very friendly and helpful, and generally better than AA. However, the food on Delta wasn't as good as AA, and they didn't serve meals on shorter sectors (even in first) where AA would have. However, I haven't flown economy on Delta, and imagine that it would be as miserable as economy on any of the US legacy carriers.
Virgin America and JetBlue do have decent economy products, and are good options if they fly where you need to go. (JetBlue of course isn't part of Virgin's Velocity program, but it's a good comparison point.)
Others have commented on the questions of luggage and lounge access with Delta and Virgin America. The only thing I can add there is that you need to be prepared to persuade the Delta lounge agents to let you in with your Gold/Platinum Velocity card. The first time I went to the lounge in ATL, they'd never seen the card before and didn't know what it was or that it conferred access; the woman looked it up in her computer and happily let me in. However, the second time at ATL a week later, a different agent asserted that the card didn't give me access; I said that if she consulted her computer she'd discover that it did, and she grumpily let me in.