I would repeat that old is not an important variable, but rather the limitations of the 421 as used as a 2 point stereo mic is important. There are pleanty of old mics that are wonderful. The 421 is a very good mic for certain applications, toms, cabs, and vocals. It will also do for overheads and flute but as a stereo pair it has limitations. I recorded some shows with these mics back in 83 and they gave great results, for the time. I preferred the sound of both the 441's and 421's over Nak 100 or 300's. But once I was able to buy a pair of 460's I never looked back. A nice pair of condensors usually have a lower noise floor and flatter frequency response. This usually allows for a recording that presents more detail and hall cues in a three dementional way, IMO. although, that is not to say that they can't make a satisfying recording........just that there are more options at the same or lower price that do a better job.
For $500.00 one can buy a pair of ADK A51TL's, used. I also have had the pleasure of recently using pair of of Cascade Fat Heads, a ribbon mic, on drums, as a stereo pair covering the kit. I was floored by these mics. Yes, they were dark and required some EQ'ing to bring out the sparkle in the highs, like many ribbons, which they had no problem doing. Man, did these mics sound great. You can buy a pair of these for $350, and to my ears they are a killer value. There are a number of other great values that can be had, too.
BTW, back to Cascade, I like the Fat heads so much I bought a pair of the Victors with Lundahl transformers. they are a long ribbon and have a more extended high end. I'll use them for a number of applications over the next few months and will report back. They wouldn't be the first mic I would go to for concert recording, since they are big, but under the right circumstance, if they turn out well, might be something special. I have high hopes for them, given how impressed i was with the Fat Heads. Sorry for the slight highjack.