I stayed last weekend for one night at the start of a ex-Dublin trip to the US. The shuttle is slightly more convenient than the Hilton airport as it runs every 20 mins and they don't charge to take you back to the airport. As IHG Spire there was no room upgrade or any other benefit other than the standard 600 points or a drink.

Adequate for a short overnight but much nicer to be Dublin proper if your plans allow.