So, plain sailing to Tiburtina, but soon after my utter lack of navigational sense kicked in! The immediate vicinity of the station is a bit sketchy, so I had to pick a direction and commit to it rather than risk looking too lost. That initial gamble was fine, but I soon became confused by a big roundabout system. In my defense, the road names were marked only by being relief-carved into pale white signs mounted on the side of pale white
buildings! Eventually though I managed to reconcile my google map printout with my surroundings, and after half an hour or so of sweary suitcase-dragging made it to the hotel: the Mercure Roma Corso Trieste. I found out later that it's barely five minutes walk to a metro station, so I would suggest that instead of the hike up from the mainline station.
To recap, this was a '3 nights for the price of 2' released in advance to Le Club Accor members (presumably all tiers?). So it came in at just a few cents under €200. Accor point earning is pretty terrible: even as a platinum this translated to just 181 avios.
Front desk staff were friendly and helpful in equipping me with a better map, pointing out the metro stop I could have used, and making some dinner suggestions. No complaints about the room either; technically had a balcony but no view to speak of, but a decent size and a reasonable compromise between price and location. Here's a couple of shots:

Bed

Reverse Angle