I say go for it. I love the Focus RS. It's a great looking, driving, feeling, etc. car. It'll be FAR better on gas, but with no less thrills.
As an M fan, you can always go back. There'll be plenty of Ms out there to buy when you're ready to get back into the game. The Focus RS is a great little hot hatch that'll serve you well.
2009 E90 M3
| Jerez Black | Extended Silver Novillo with Brushed Aluminum | 6MT | EDC | Premium Package II | Convenience Package | Enhanced Premium Sound | HD Radio | Heated front seats | Fold down rear seats | Moonroof | 19" wheels |