Power Cord; upgrade vs tweak

I have a no-name tube amplifier in my bedroom for music listening(it is black, has 4 tubes, rated at 30 watts and actually has no name on it that I can find). I bought this amp at a garage sale and all the info I get from it is written on the case. A friend of mine guesses that amp brand new was probably about 400 dollars, if that much.

It has an unremovable, molded power cord. I have never tried power cords before and I thought it would be a good test to see exactly what a after-market power cord can do.

My question is; would it be better to upgrade to a better amp with a removable power cord or tweak the amp I have and get a removeable power IEC setup?

When can someone tell when to choose an upgrade over a tweak? Is it just money?