Right, you don't need to tip the doorman per bag. Tip the shuttle driver $2 per bag, tip the doorman maybe $2-$3 total, then tip the bellman who brings the bags to your room $1 to $2 per bag.
I travel with a total of 5. On vacation, we can make the first contact work for the $5.

To me, it's also about the class of hotels and the convenience. When you stay at the Grand (or even DLH), you are staying at a luxury hotel and should realize that the bellmen (wish there was a gender neutral term other than the antiquated bellhop) are part of the experience. You should also realize that unless you have a later check in, the bellman can help smooth things over and that they are generally giving a great service.
Paradoxically (and probably due to pay scales at different resort classes), I find the bellmen at the mid-class hotels more aggressive when I choose to carry my one roller bag that fits under my airline seat rather than have them bring it up to my room.
Do we need to tip the shuttle person? 