Neat that you want to save your favorite bike.
It makes totally sense why you want a new bike, even if this is your favorite of all time. While a drivetrain can be changed to match the terrain, a tire size can't always be changed. 25mm tires on stone paths and gravel isn't ideal, so retire this and buy new. Makes sense.
...entombing your favorite bike is the confusing part. Why not clean then and hang it on a wall for you to see and enjoy? Placing it in a coffin just seems to defeat the purposes of a bike(to be ridden or admired).
But its your world, man.