That's exactly what my ailing beater is: a steel rigid mtb from the 90's with narrow slicks. For a beater, that's my favourite style of bike: cheap, versatile, sturdy. I like it so much in fact that I have another partially disassembled bike like that lying around that I bought used for rather little cash. But for my new bike I want something... new... and different. But as you do say, it's not a bad route for the budget-conscious.