Both of your comments are very interesting to me. I only ponder this question of who really owns this house becaue of the way the owner is described, but not named in the first chapter of GOF.
It states:

"The wealthy man who owned the Riddle House these days neither lived there nor put it to any use; they said in the village that he kept it for "tax reasons," though nobody was very clear what these might be. The wealthy owner continued to pay Frank to do the gardening, however."

this indicates to me that someone very wealthy (like the Malfoys) owns that house and not Frank. Could it be where Voldemort hides out or where the DE meet up at? These are thoughts that go through my mind. Is there a reason that the owner wasn't named? Is the owner or the house any signifigance to the rest of the series?