Does the term track guidance apply only to conventional procedures?
ICAO Doc 8168 "Procedures for Air Navigation Services - Aircraft Operations - Volume I - Flight Procedures" states under 2.1.3 Types of SID:


  Track guidance may be provided by a suitably located facility (VOR or NDB) or by RNAV.


To answer your question: RNAV/RNP SIDs are considered procedures with track guidance.

The better your tracking is the smaller the protection area required (especially for turn construction). So flying inbound or outbound a navaid or having RNAV capabilities greatly increases your precision und therefore allows for procedure construction with relaxed climb gradients in areas with difficult obstacle situation.