Loan financing with building savings contract

Hello everyone,
I bought a condominium in 2006 and secured the loan with the bank using a home savings contract. The contract with the bank runs until 2016, but I can (free of charge) repay the loan early with the allocation of the home savings contract.
I would like to use the loan until the end, but the interest on the home savings contract has become so high by now (which is good...), that I will soon reach the saver’s allowance.
Thus, I have "no room" left for other savings investments without having to throw the withholding tax to the state.
Does anyone have an idea how to behave here?
By repaying the loan with the home savings contract, I would initially lose the "credit balance" and could invest money more freely again, but on the other hand, at some point the apartment will be fully financed and I will also have to pay taxes on rent and leasing... That’s why I would like to keep a certain "debt level" on the property...
Regards
deichkind

Well, you can't have everything in life.. There are also types of investments without interest, so you don't need taxes on those.. and besides, there's always the question of how much tax we're actually talking about here..