If your DM is not permitting Mighty bows, then Archery is a much less viable path. Even on my 10th level archer with magic buffs up the +4 dam from the mighty bow is 40-50% of the damage bonus.The weapon mastery feats (from PHB II) at higher level are terrific, but that's not til lvl 9 or 10.
A dip into ranger is a good idea for the bonus feats (archery path), skills and favored enemy. Sounds like the DM won't let you take anything useful for the Favored enemy though.