It sounds like you’ve done the 1968, "Switched-On Bach" thing on your own. It must be fun to play with old classics and modernize them in some way or another.
While it is not a case of classical music it is an example of an old song updated but look what Jimi Hendrix did with the Star Spangled Banner at Woodstock.
Another few examples, though not of songs as old as the Star Spangled Banner would be the Van Halen/David Lee Roth versions of "That’s Life" and "I’m Just a Gigolo" and "(Oh) Pretty Woman" and "Dancing in the Streets" and ZZ Top’s version of "Viva Las Vegas."
A good group can cover just about anything that was good if they are imaginative enough give it a new sound but still retain enough of what made it a hit in the first place and have a hit of their own.
Quiet Riot did it with The Runaways
"Mamma Weer All Crazee Now," though I admit that is not a good example because it was a rock song to begin with and just covered but it does show that if you take something good from the past, far enough back in time that it is not familiar with your present day audience, and do it well you have a hit on your hands.
Music is like so many others things, and maybe even more so in that quality lasts, it is something timeless and it does not really age or become dated.
Many songs of the 60's and 70's that were big then now seem really dated and just do not work, like most Emerson, Lake and Palmer songs, but some are as fresh today as the day they first came out and that is because that had something special to them, something that does not lose its power and feelings over time.
A group can have a number of gold and platinum records and in ten years or more people hear them and want to stick their finger down their throats and puke but songs like "Sympathy for the Devil" live on and on.