One point about restoration of paperweights is that if a domed weight is reground and polished then the profile can be altered such that a significant visual degradation results.
This usually means that design elements at the outer edge, especially millefiori canes, can be, at least partially, lost to sight (sometimes referred to as "falling off"). Where a weight has had a partial repair to the dome, rather than a full regrind, then the design elements can be off-centre when viewed through the top of the dome.
Another problem is where a domed weight has been restored to the top or side of the dome only, resulting in a "flat spot". That type of repair can cause a reduction in the magnification of the design at the area of the the repair.
Any repair that causes an obvious distortion to the internal design or pattern can give rise to a serious reduction in monetary value.
However, where a repair has simply been a light grinding and repolishing of the whole dome in order to remove surface scratches, the result is usually an improvement in the visual appearance of the weight. In such cases, the monetary value, compared to that of a perfect, original example, will not be greatly affected.
Many antique French weights (which have developed a cult status amongst some collectors) have been reground and repolished at some stage in their history but are still desirable to lots of people and therefore command sale prices not too far below the "price for perfection".
For myself, focussing on Ysart weights, I have only had one item repolished and that was because of heavy scuffing and scratching to the dome. I bought at auction it before I had even heard of the name Ysart. Nobody in the room wanted the scruffy looking concentric item and in reaction to the auctioneer's rather forceful tone, I raised my hand. It was mine for £20. In its repolished state, and with its proper attribution, I am sure that somebody on eBay would now be happy to pay at least £200 for it.