I am the holder of a delta reserve card (as well as a PM), and while I have no proof that it gets me upgraded more regularly than those without it, I am fairly sure it does. I bought mine because I am constantly on hub flights with a million other PMs, and always buy T fare tickets, and so was not getting upgraded very often; now at least I beat out the other T fares for the upgrades.
Other notes about the card: Once you have the card, your skymiles account gets a note next to it that says (in my case) "Platinum Medallion | Delta Reserve". -So it at least registers with Delta that you have the card; which leads to the question if you actually have to use the card to purchase the ticket to be eligible for the priority bump, or if just having one is enough. I have never gotten a satisfactory answer and so I always use it to buy my tickets just in case.
Also, as reported, you do indeed get access to DL skyclubs. They will ask to see your boarding pass in conjunction with the credit card.
As for the shorter security lines, many airports with dedicated DL terminals (such as LAX, JFK, ATL, etc) will allow medallion members access to the fast line (it says 'elite' on your boarding pass) always. The card won't make any difference as far as I can tell.
Next up, the delta card offers you a 'concierge service'. I have never found a great use for this to be honest, but sometimes whenever I get sort of annoyed at how much the card costs (when the bill for the yearly fee comes), I will call them up and try to get them to figure out ridiculous things for me, such as converting common units of measurement into obscure ones (" can you tell me please how many leagues make up a mile, how about farthings"... you know, stuff like that).
Finally, you should get a companion certificate after year one, good for 1st class domestic RT travel. So thats something.