I've been reading the posts with interest, This is a purely personal view based on races I have ran in both small and large over the past few years.
I ran in a small race 2 weeks ago. It was the 7.2 miles road race at the 120th Much Wenlock Olympiad Games. These Games have a history going back to the 1850s. Just 65 competitors took part in the race, staged on a picturesque and hilly road course. The event is very welcoming to beginners and experienced runners alike. The marshals and organisers were friendly. The event was very well organised - better than some of these big events. There was a water station, and at the finish you got a medal and a bottle of water. There were also cheap snacks/lunches at the event to buy.
This is typical of small events. Contrary to popular belief they are NOT solely the domain of elite club runners. Most events attract a wide cross section of abilities and are very welcoming. This event cost just £2 to enter. I did it in 2004 and I will definitely do it next year as well.
For your information, the most I have ever paid to enter a 10K is £7.
OK, some events I guess you've just got to do at least once (e.g. Flora London Marathon; BUPA Great North Run) but taking the GNR as an example, why should I be stuck in an overcrowded race where I have no chance of running to my ability, and pay through the nose for the privilege. I have never done the British 10K, but I get the impression it is a similar story.
Whilst I would do Flora London Marathon again (the organisation is very good and I was able to run to my pace because of the seeded starting pens) as for any of the other big "charidee" events, I say forget them and support smaller events which in my honest opinion are far more welcoming and friendly. A lot of these events also have a charity angle to them anyway - for example, I ran a half-marathon in February (£13 entry fee), but a portion of that went to some local hospital.