It might be interesting to look at the original (and any subsequent published) light curves of these proposed planetary systems to check what the unexplored orbital period/transit depth space looks like? For example why would HATNet have not found the other potential planets in the HAT-P-19 system listed in table 2? Also, in additional to the effect of inclination, it should be possible, given a maximum size of planet and a minimum detectable transit depth, to estimate the maximum orbital period it is worth looking at for each system.
Interestingly, there is another similar proposal currently being discussed on Stargazer’s Lounge. They are planning to look for very shallow transits to 0.1%, though I am not convinced that amateurs could do this for transits of unknown timing and duration.