If ALL you want is a new bar and grips, it probably wouldn't make much sense to move up to the 7.3. I've ridden the PDX, 7.2, and the 7.3 and I didn't think the bikes where all that different, really. Just ever so slightly better components all around. Might be a big deal for some, but for me it just came down to the color/disk brake preference.
If I recall, the 7.3 had very similar bars as the 7.2. For $130 there are some nice bar options out there. You may not even use half of that. If you want drop bars though, you may consider a different bike as it could be pricey converting it over.
Hope this helps.