With current rates, I'd say pulling money out is a good idea. Historically the cost of money has been much higher, and getting money to play with for 30 years barely above inflation seams like a good idea. This is something I've been doing... cash-out refi on two properties gave me a downpayment on a 4plex that allowed me to borrow several hundred more at the good rates.
Tricky part is assigning that debt to something worth while. I know one person who took out a HELOC to reinvest, and ended up buying some big toys, paying for travel and other things, and now the house is underwater with no income to show for it. So.... as long as the income from future investments covers the cost of the new cash.... and as long as you have enough of an income margin to handle any market corrections.... I'd say go for it.
Note: It's probably less stressful to go the other route and pay things down as you move forward... so if that's important to you, go with that... some things are hard to value.