Upgrading the panel seems as though it'd be expensive, but I imagine it'd be like nothing compared to upgrading your incoming line.
The electrician told me that for an above-ground line, it isn't that big a deal - utilities replace lines all the time when trees take 'em down. Utilities apparently often upgrade old ones for free when they have to replace them after storm damage.
We are usually thankful that the line is underground - it means that trees don't take out our power in blizzards and nor'easters. But for this, it is a bit of a bear - cost wise, it would be far cheaper to swap the house to an above-ground line.