From reading forum posts it seems you can got obscenely wealthy with some of the buildings, so I've avoided them and know nothing about it.
I don't know about throwing items, are you thinking grenade team? Fun! Not sure if it works, try it out. Let me know when you find out.
Yes, buy yourself a bunch of pickaxes and shovels, and toss them in the chest, but carry a couple on your person. So far I have found 2 uses:
1) Sometimes, when you talk to people in town, they will offer to sell you a treasure map. Often the price is crazy unreasonable, but I've seen it at under 10,000. If you get a nice low offer, buy it, follow the map, and you might find treasure. Sometimes they require a shovel, sometimes a pickaxe. Sometimes there is no treasure at all, but the chance isn't related to price, so only buy at fairly low prices (not sure when exactly it is worth it, I think it would depend on player luck, but under 20,000 might be worth it? )
2) In the maltese crypt, there are 7 buried treasures that you can dig up with a shovel
(but be careful with the maltese crypt for now. It is VERY glitchy, and you can't spend more than 10 minutes in there without things going haywire. Standing motionless corpses, enemies becoming immortal, the script for added hp breaking down so all enemies die in 1 hit....It also has severe balancing problems, and you can make several hundred thousand gold trivially, or worse, you can accidentally run into mist that permanently raises your HP. Coming out of there with +50 permanent HP is very easy to do without really trying, just by bumping into the mists now and then, and it is unbalancing to the rest of the game, where HP imbalances are supposed to be part of the difficulty. I am going to try to fix the problems with it later)