I'd watch a senior tour. It should be mostly recent retirees, so the tennis would be as close to tour level as possible (although some more distant retirees, if in shape, can join too). And I'd like to see an actual tour, with a series of tournaments over the year. And negotiate with the slams to make their seniors events a part of this tour, much like the regular slam events fit in with the regular tour.
It would be nice to see a combined seniors tour, but I wouldn't hold my breath waiting for that one. And failing that, the individual tours could be held in conjunction with existing regular tour events (Tier 3 and 4 on the WTA, and whatever they call the equivalent on the ATP.) The senior matches could fill in the late schedule, to give the fans extra value for their tickets, and save the regular tour players from having to play, say, doubles late at night, then come back the next day.
They should get their own ranking system, and hopefully their own sponsors. (Or perhaps some extra contributions from existing tour sponsors.)
Players like Sabatini, Novotna, Date, Sanchez-V, Tauziat, Zvereva, et al, can no longer challenge for the regular slam singles titles, but can still produce some good tennis.