Refinancing - There's isn't enough information for me to provide specifics...so, I'll address it both ways. 

Like many I refinanced in ‘20 and locked in a 2.8% rate on my current property and I assume it can cash flow around 400-500/month if rented, or 125-140k net on a sale. 

If the note is refinanced immediately we increase our net worth by $685,000 instead of $450,000.2.

I know it'll significantly increase the value of the property by making 4 total units on the lot, but refinancing out of my 3.75% interest rate seems like a huge bummer.Thanks in advance!

With a 30-year amort and 10-year IO options - as well as ability to get rate down quite a bit if you have long-term horizon (5+ years so don't mind prepay) - the rates/terms and monthly payment will likely be very attractive.Others too have done the DSCR Portfolio Loan (Blanket Loan) refinance option too (refinanced the 10 properties that are under conventional into one blanket DSCR Loan and start the process back from 0 on conventional), however, given current rates, don't see it a lot currently since the refinance would typically mean racheting up interest on those

What's your goal with refinancing?

A few things here. 1)Refinancing a loan (conventional) into another type of loan (DSCR) does NOT lower your debt to income ratio in any way.

@Ronald MejiaI like the idea of doing it all cash and then refinancing it.

I refinanced multiple times to both get cash out and lower the interest rate. 

My non-laywer advice is to get that thing refinanced and read the mortgage docs before you close and abide by the terms of the contract.