First off you have to remove the problem not the symptoms. Start replacement characters at the level of the lowest level survivor. Eventually they'll balance back up again for you. Let's face it, a penalty for dying is just as artificial as any of the solutions that attacks the symptoms, so lose it. What are you really discouraging, anyway?
I assume that after so much time playing the game that the players are beyond doing stupid things (mostly

), so that can't be the reason. It causes YOU more trouble than it causes them and those troubles just get greater as the campaign moves along further. It stalls the campaign, which isn't fun for you or the players. Another problem with such a penalty is that it discourages acts of bravery in hopeless situations which takes away from the heroic nature of the game. Once the whole party has run through a handful of deaths, they'll all be back to the same level and dying simply brings them back at the level of the whole group. Win/Win.
To bring the wealth level back in balance, alternate treasure seems to be in order for a period of time. A "coupon" solution can be useful but need not be overt. Have the group find expensive items that (perhaps after some divination) are discovered to belong to someone that wants them back, I.E.
the chalice of Soenso, the honorable Baron of Zumplaize. Such items can be engraved with the name of the rightful owner or the heirs. An item can come in a case or box with an inscription denoting its owner.
Returning such items can entitle the party to medical assistance from the baron's staff or free but incredibly lavish lodgings next time they travel through his territory. Other such items that need to be returned could gain the party valuable information, a free resurrection, the goodwill of a small army that will pledge to guard an area for them sometime down the road. Make treasure more along the lines of barter for favors anytime the wealth level is out of whack. Once it is back in line with the standard, start handing out normal treasure again.
Another way to reduce PC wealth is to have unusual economies. Nibble away at their wealth with prices that are 110% - 120% of the standard. Any place where there is some sort of excuse for higher prices, such as a region where the taxes on merchants is higher, is a good reason to raise prices...but not so much so as to raise the alarm with players that you are milking them. Over time it'll put a dent into things and if it is done judiciously it won't seem like a personal assault on the PCs by the DM.
Equipment needs regular replacement. Heels break, straps snap, and (here's a biggie) mounts are not immune to attack. Maybe they’ll use mending spells but wealth is not the only resource that can be drained to help bring a game back to balance. Also, when creatures attack a camp they don't tip-toe through the gear that is lying all around and things should be broken fairly regularly. You don’t have to describe each and every bit of the destruction, just be sure to give them a description of the aftermath. If the players don't like dealing with this in-game, simply explain that they can either buck up on some sort of regular basis or you can do the bookkeeping and reduce treasure amounts a tad to compensate for such loses. Then, do so.
The price of information is never written in stone. NPCs have
detect magic and when they know that a group is well-heeled they will take advantage of them. Find opportunities to present the players with a choice between knowing something for a high price, or going into a situation blind. They won't bite all the time but when they do they won't complain because the choice will be their own. An NPC that steals from PCs is in danger of retribution but an NPC who talks PCs out of their wealth by selling them something they want is someone the PCs may visit whenever they have extra wealth and need information. This then becomes a semi-regular way to help you drain some wealth from the PCs.
Where do the PCs call home? Do they tithe their respective church? Does the local nobility require service of them on a yearly basis...or in lieu of such service are they given the choice to purchase their way out of it? Standard fare would be to suggest the PCs need not guard a border for the Duke if they pay him enough so he can hire regular guards to substitute for the service they owe him. They can make "in kind" donations of magic items and there's no reason for a noble not to ask for specific items after having his minions determine what they have. If they don't wish to part with the 5,000 gp item he covets, he may begrudgingly take two other items that total 7,000 gp in its place. Again, it becomes a negotiation that plays into your hands and it is something the PCs have a hand in determining so they shouldn't feel as bad as if you just rust monster them out of an item.
It's been my experience that single, quick fixes lead to more problems so what you need to do is get into a regimen. None of the tools should be used in a heavy-handed way. No single method should be seen as
the one solution. Take back what they should not have piecemeal with a variety of the above ploys. After a short time, when things are back to balance, you can keep it that way quite easily.