As one with many years in the catalog business (Didn't know Zazzle was a catalog?), here are some thoughts.
There are many factors that affect your position in the marketplace and each has an influence of varying degrees. zRank is just one.
zRank most likely will not outrank sales, for example. Other factors that influence your position in the marketplace include views, comments, date created, total revenue, units sold, product reviews and others I can not even think of. Combine those with a recency factor and your head starts to spin. At one time, and perhaps still, your frequency/recency of product creation was a factor. Dizzy yet?
zRank is just one more item among several factors in the algorithm and its strength has yet to be observed. I suggest that any factor having to do with sales will greatly outweigh zRank. Zazzle has said that zRank will affect your position in the MP. Well, an effect of 1% is still an effect. I suspect that whatever the influence factor is, there will not be a dramatic shift in the marketplace except for spammers. Zazzle will never tell us what the influence of zRank is, so we must wait and see.
We will wait for this zRank stuff to shake out before we make any big and drastic moves. This will not happen until zRank is really live such that it is affecting the marketplace (Sad that Zazzle has not said when). And even then, it will take perhaps four weeks to see what sales impact if any zRank has had by comparing to past months results.
We are watching an interesting set of posts regarding the ratio of live sold to live unsold products and their impact of zRank. We think they could be on to something. Our main store has about 2,000 iPhone3 cases made many years ago with no sales and virtually no views. I would have no problem removing them.
For now, we are going to finish up getting our store stats up to 100%. Clearly store stats have little to do with zRank. But it is simply a good idea to put your best foot forward. Between that, some new product creation and sprucing up for Christmas sales (They have already started, by-the-way) there is plenty to keep us busy for six weeks or so.