We've met quite a few who have done it and none regretted it. I do wonder though why people spend money doing it in company when they miss out so many nice places like the French west coast and the Rias.
Did the Rally in 2010. Great for setting a departure date and forcing us to get ready to go, helpful info from Rally team re preparation, safety etc, great help in having berths arranged along the way and IIRC Rally fee paid for by berthing fees, Rally team very helpful with local repairs/services, great welcome/support from marinas by being part of rally, great to meet other crews, good social events including inland visits, and kept us going at reasonable pace down to Lagos so ensured we got well on our way to the Med - otherwise we may still have been in France or Spain! Downsides? Sailing to the Rally schedule - we would have liked to spend more time in Galicia and on occasions without the Rally schedule we might have waited a bit for better weather. Overall think it was great for us as we are novices.