Is my septic system holding me back?

[James Alderman]

Hello BP community, I have a 5 bed 3 bath cabin in the northwoods of Wisconsin. When I purchased it, the sellers only listed it as a 3 bedroom because the septic system is 1000 gal (rated for 3 bedroom home) and it lacked egress windows (already fixed). I'm considering adding another tank and more drain field so that it is properly rated for a 5-bedroom home, and I can advertise it as such.

My question is this: how much value would this add to the home when it comes to selling? Break even or possibly gain more value? The home itself is Class A with high-end finishes. Buyers in this market are mostly families from Chicago looking for vacation homes. 

I know, there's a lot of nuance with these things. Even so, I value your opinions and want to see what you think.