SIDs and STARs aren't mandatory at all and RNAV procedures are flown basically the same as VOR procedures with aircraft equipped with an HSI or VOR receiver. Obviously you need a GPS unit(or an old school rnav device) but you will shoot the needle the same as you do with VOR, you just wont have to dial a frequency and monitor the dme(btw, a GPS unit is a legal substitute for a dme according to the FAA. Obviously it refers to approved gps unit like the GNS and not your mobile phone)