I've looked into this myself quite closely. I average around 60 hours a year or five hours a month. There was a share in one of the aircraft at my club going for around 4K ish subject to haggling. To break even over renting I would have to do 3 hours a month or more. The availabilty was/is excellent, aircraft has a very healthy engine fund and it's a full IFR fit go places type machine. You would think it's a no brainer but...I like to fly different aircraft.
Now when I was a golf nut I used to play all over the place. I finally bit the bullet and joined a local, quite expensive club. I never played anywhere else after that because I had paid my money and was damn well going to use that club. I have a feeling that having a share is the same, I would fly that aircraft to the exclusion of everything else. I currently have access to seven different aircraft types, not counting the sub types within those. I enjoy getting in something different so in the end I decided not to make a bid for the share. It costs me around £50 a month not to be in the syndicate and fly the hours that I do. I reckon it's worth paying that.
However, you have to make your own mind up. Some people just like having a share in an aircraft and hardly ever fly it. They are the people who you need in your syndicate!