I wasn't all that happy with the YC concierge. I've stayed at YC, BWI, GF, Poly, and AKL concierges, and YC was towards the bottom.
The staff was generally disinterested, had a HUGE roach on my suitcase (not a palmetto bug), power went out during stay, lounge was stuffy and formal, I just didn't like it.
It was more formal than BWI. If you really love the Poly you will probably not care for the YC. Where the Poly is friendly and casual, the YC is stuffy and formal.
Anne