You need to look upon share ownership philosophically.
If you want iron clad no risk agreements then you have to rent. But you have already pointed out all of the downsides of renting which leads you into the murky pool of share ownership.
I, like others, have been involved in several shares. The availability in all of them has been pretty much unlimited. As Gengis points out usually fewer than 25% of pilots put more than 5 hours a year on the frame. In one of my syndicates 6 out of 16 had lapsed licences. They pay, you fly.
Re agreements, for less than 10 k just write it off but you are likely to get all your money back when you sell ( or more.. Try that with a sports car!). There are agreements but I guess some will be tough to prove in court. The way I look at it is if I bought a £60k airframe ( or sports car)I could easily see a £10k bill at the first annual. Any money I get back on that 10 k is a bonus.
The best thing about syndicates is you get almost 100% of an airframe for a fraction of the cost and you get some very clever fixing knowledge. Do it and advance your flying.
Oh and buy something realistic. 152, 172, archer Cherokee, warrior, arrow. Buy something tidy, if the seats are ripped would you girlfriend be confident in flying it ( remember its girlfriends and wives who get a say when you sell). Also learn what TTE means, if it's near 1600 then there's a £20k bill and 6 months on the ground looming.
I have to conclude by saying I have had 5 fantastic syndicates. Even when an £8 k bill hit there were 16 of us and a fund so it cost £350 each. All the rest I've not had a surprise and I've had flying that cannot be easily rented(Cherokee, DR9, Pitts s1, Pitts s2, RV6). Now looking for an RV4/8. Syndication is the way of the nation.