I disagree with this number, many people have said it respawns for an hour afterwards, but again, from my experience destroying half the town, this respawn time was more like 20 minutes in every single case. I or a guildmate hung back to collect respawns in every case and never once did anything spawn after about the 4-5th spawn which was about 20 minutes after the explosion.
I admit I'm not rares collector, or seer, but I can see certain pieces of rubble actually rising in value over time, of course the general junk will be close to worthless, but the items that only had 1 copy present on each facet/shard and have previously un-owned graphics will have a mid-high range of value as people put together their collections.