In Finisterre I met a young Malaysian pilgrim-to-be, who hadn't begun yet. She only had about ten days and was going to walk the last nine stages of the Camino, bussing it to her start point. I advised her to avoid Sarria to Santiago and instead do Astorga to Sarria.
For me walking those last 110km was a rude awakening to school party and tour group hell, and was really jarring after such a beautiful previous four weeks. Much of the community spirit seemed to evaporate overnight on leaving Sarria. No-one greeted each other with "Bon Camino" any more, cause there's so many people you'd never stop saying it. We arrived in a Portomarin that had been booked out by school groups who weren't even doing the full Camino, just a two-day hike, but still causing the city to have to open overflow shelters for everyone else.
My point is, when you can experience this sort of crowded touristic hiking anywhere else in the world, why choose to spend half or a third or your limited Camino time doing this bit, just so you can get a certificate? Forgo the compostela and get stuck into the earlier stages, I say, where you're far more likely to have profound personal and spiritual experiences. If you're not doing it for Catholic reasons, I see no reason to see the last 100km as obligatory.
I'm pleased to say she took the advice and had a great time, reporting back that she definitely made the right choice, so I'd like to offer up the idea here to any other future pilgrims who are on a tight time budget