But there are plenty of surviving examples of period art with what appears to show smooth surfaces.
Edit for clarity: I'm most interested in the period 1000-1500AD, plus or minus a bit.
So, here's what I'd like to know:
1) Apart from the examples posted below, can people post examples of period sword scabbards that are decorated? Not just decorative metal work, but tooling to the surface of the body of the scabbard.
2) What hard evidence do we have that scabbards were more expensive (in some cases) than the sword? This is cited every now and then, including by scabbard makers justifying their prices.
If we can nail down some particulars perhaps we can begin to see if scabbards were tooled only in certain periods (like the early 14th century) or only in certain ways or in certain amounts. Modern reproductions sometimes get into sweeping scenarios like: If some scabbards were tooled, it's appropriate to tool them all. Or: If some scabbards were plain, it's appropriate for all of them to be plain. We can do better than that. Please note I am interested in historical data, not modern preferences.
I'd like to see if we can dispel some notions and get some good factual info. :)


Robert (or William, depending on source) de Setvans, 1306


From rubbing of Robert (or William, depending on source) de Setvans, 1306. Better detail


Sir Roger Trumpington, c. 1320. Heraldic shields down the scabbard.


Sir William FitzRalph, ca, 1323


Baron Camoys, c. 1419. Diamond shaped decoration?


Edmund Clare, c. 1488. Simple pairs of lines