We have the same issues regarding empty plot on our site (which is huge) too. I think people take them on imagining a Monty-esque kind of life ...no disrespect intended... without realising the graft required. I wish there was a kind of mentorship approach available for newbies to help them get going and keep going
And as for value, a full plot here (10m by 25/26m) is £79 a year with reductions for people who live in the borough, and further reductions for un-waged or pensioners, meaning I actually pay just over £11 each for my two plots. Value? Well obviously
The year I took on the second plot, buying wood to edge beds, a 3m x6m polytunnel as well as all the usualt stuff, I painstakingly kept track of al expenditure over the two plots, and costed all harvests as "Tesco rate" as that seemed a more reasonable way of doing it than organic veg prices (even though they are) and at the end of the season, there was a theoreticala profit of well over £200. I know I never would have bought that amount of soft fruit, but it just gave a bit of a guide. Felt comfortable then to invest in a second tunnel too!