I think it really depends on your mission...
If you're flying a vintage plane for the love of vintage aeroplanes, and do so in your spare time during the summer, then why install anything but the original instruments?
If however, you love the aeroplane, but it is your main "go places" aeroplane. You intend to fly in IMC, along with all sorts of possible conditions you might encounter throughout the year - then in my book, suitable instruments would be preferable.
If you wanted to keep the original "look" you could probably hide the new part of the panel with a removable cover, which you can remove in flight to reveal your spanking new G500 with SVT, terrain etc... and a GTN750 in addition to an autopilot! (well okay... maybe overkill - but you get the idea!)