One little suggestion how world travel speed could be boosted. In cities, there could be NPC trapper. After talking with him (some minor quest, bring him something, pay him some fee, good karma, reputation, whatever), he would give you a temporary boost to your world travel speed. In real world you can imagine that like he give you advice about local patches, weather, raiders movements, that could help you to get more safer and faster thru wasteland.
This would make this NPCs very popular and it could make meet and chat places in other cities than NCR.
p.s.: it could be related to speech.. if you have some level of speech, you are able to use service of this kind of npcs (plus quest, ....).