Thanks all for the advice. I decided just to upgrade the tubes for now. I bought
EH6CA7, RFT 12AT7, and RFT 12AT7. I am really looking forward to hearing how they sound compared to the stock tubes.
Re: upgrades -- the only thing I did so far was put in a better power cord. Power supply in the house is ok. Still need to rewire the house for three prong outlets so I am still using a dinky converter from Rite-aid for the plug.
One of these days I may do one of the more expensive mods but for now, figured I would rather swap tubes ($150) rather than a mod that would run up to $600. Maybe in a couple of years.