Usually I spend a few hours exploring dungeons and then several more fast travelling around for merchants. I think the economy should be a little more dynamic.
Below is just a few ideas I had. If any of these have been mentioned before or are in use, I apologize.

Set a total amount for the gold all merchants in Skyrim have. Basically a pool. Based on level, gameplay, and certain conditions this level can rise or fall.
As you play in a certain area and visit the local merchants, gold gravitates there. So if I sell a lot in Whiterun, then more gold is located there.
Gold levels increase based off of the movements of heavily armored merchant/caravan convoys. These differ from the caravans we know as they carry less specialty items and move items from town to town. As they travel, their interactions increase the total gold levels. If you kill them, you gain quite a bit of gold and items, while also increasing infamy greatly (but only if there are survivors or witnesses, frequent merchant deaths will cause guard patrols and/or mercenaries).

These convoys re-spawn slowly and certain specialty convoys will not re-spawn at all (named vs generic EX: A blade dealer vs a general merchant). Killing a convoy will yield a lot at the moment, but slow economic growth. Also, killing these convoys will slow the gravitation of gold towards certain areas. Border towns will receive certain perks based off of the perceived advantages. A more metropolitan city may start with higher levels of gold, while something rugged like Riften may have lower levels.

The idea is that as we level gold amounts increase. And to prevent merchants from running out of gold, gold gravitates. This creates a more realistic setting, fixes a problem, and makes players feel like we actually changed something. Case in point: we become thane but nothing really changes. Maybe a guard say greetings, but thats about it.

Additional functionality may include having certain named merchant families that offer minor quests for distinct bargaining advantages. EX: This shopkeep owes me money, or this competitor is undercutting me so eliminate this convoy.