AFAIK the valve is there to to stop the heater matrix rupturing if there is a cooling issue or overheating, a safety/CYA thing as front passengers would get scalded. If the cooling system is up to scratch and maintaining temperatures within tolerances it won't be strictly necessary.
The gurgling sounds like there is still air trapped in the system, so the best way is to make sure that it is bled out when refilling - I tend to refill first, leave the reservoir cap off and start the engine and let it warm up, squeezing the top and bottom rad hoses every once in a while - when the stat opens it will take a big gulp, so you'll need to top up quickly, check the hoses again, then put the cap on, go for a drive, let it settle and top up as needed to get the correct level. The coolant is pressurised when hot, so be very careful when opening the cap - let it sit for a while.