Just finished to read a PhD History work on Roman-Dacian Warfare. Inspiring.
I think Dacians could be more differentiated from others barbarians with these suggested options :
1) Special leader, 0-1 Decebalus with Stratagem rules.
2) Non Falx warriors could have the option to get Evade rules as for Spanish units.
3) Allies could be up to 50% to depict the great counter offensive in moesia in 101 CE (With Dacians, Bastarnae and Roxolans (Sarmatians)).
Dacians were great opponents to Romans, for those who could doubt about it : Caesar prepared conquest of Gauls with 4 Legions and fougnt at Alesia with 6 of them. Trajan had 10 Legions to invade Dacia !
The great difficulties of Trajan were about Dacians warfare full of ambushes and surprise attacks (so stratagem and evade rules).
Hope this would help for a more historical list.