I'm too lazy to log every single TU I spend/gain from each specific transaction I've made.

It's not like bank history, but that's included too.

It could be like a new module for the profile or a new page for the site in order to view one's profits/losses.

You view your whole spending history and it could be color coded like: Teal for buying from Res Shops, Red for buying from User Shops, Gray for those little random TU that pops up every now and then, Blue for actual bank transactions.

At the bottom, it could have your own portfolio summary. It totals up your profits and losses. I think it's good to have a log of that somewhere, especially if someone wants to know how much growth they're having or lack of. 

Something like that. I'm sorry it's vague; I'm really tired at the moment. But I'll try to explain more if you have any questions. ;o;