I've had mixed experiences with guides. Last time we were in Rome, we stayed at the Hotel Eden (Dorchester Collection) and had the concierge arrange for a guide for a couple of days. They charged us a lot more than if we had arranged something ourselves (like 4 digits in euros) but the guides were merely OK and absolutely nothing exceptional. One of them had even totally screwed up the booking for the coliseum and so we missed out on that.
And itīs all very easy to visit on your own..... especially if you use a Roma card