Since you know the area, I'll give you the geographicals.
When I lived in Concord, I couldn't hit the 2m220 529 box on Tam handheld or in the car very well in the Diablo Valley.
With the cross band repeat, the 529 box would receive my input signal through the Hustler G-7 I had at the time, while I was using a 220 ht (I had a Kenwood TM-621A). I could walk around the house using this radio:
Kenwood-Trio_TH-31BT.jpg which was only 1.5 watts.(the photo is the 2m version. The 220 radio looks exactly the same)
In the car, I had another 621A which I used crossband to access the 2m box through 220.
The only problem was the repeater would have to totally drop in between transmissions, otherwise it wouldn't work. As you might expect, the local yahoos would figure out that you were using crossband repeat and would make sure the repeato would never drop.