Cash out is probably a better way going forward. If you do HELOCs, they can screw your credit up if you borrow 100% of them just like maxing out a credit card. The flexibility of a HELOC is nice but they shouldn't be maxed out long term.
How long have you had the 80% loan? Seasoning is different for different banks. Sometimes it's 6 months, other times it's 12 months. Before the seasoning period, they only want to give you original purchase price. After that, they will base off of appraised value.
A cash out refinance only requires 6 months seasoning and you can start the process prior to the 6 month mark. Keep record of all the improvements if need be to prove the value increase.