How many? Geez...to my recollection, Dwarka has had about eight official expeditions, not counting the current university group over there. I think the first two were mostly geologists, but pretty much all the ones after that were archeological studies, so I would guesstimate, maybe a dozen archeologists, over the last three decades? Somewhere in that general area? Depends on which part of the site is accesible, mostly.
Mahabalipuram, being a World Heritage site and visited fairly regularly by tourists, has archeologists working regularly, so over a dozen, easily. The Archaeological Society of India (I forget the official name) has been pushing it lately, after the 2004 tsunami uncovered some incredible new structures.
Yonaguni has been pretty much decisively shown to be a natural formation, which doesn't make it any less cool, but right now, tensions in that area are a bit high, what with China making noises over the Senkaku Islands and all.
How are you defining "ignored"?
Publishing actual research on it. You won't find that in the Fiction section of the bookstore, however. You will have to go to the Science section. Or the travel section, in the case of Mahabalipuram.
Don't you think, prior to assuming that no academic has ever investigated something, it is worth spending a few minutes on Google to see if any academic has...well, investigated something?
It's like you want science to be the bad guy.