The really skillful sellers know to sell multiple items in their threads – and to encourage questions – auto bumps. Of course there is a certain point beyond which there are too many, or too many useless items in a sale thread and the pain of actually looking at the sale goes past the critical threshold. Diminishing returns. I'm sure someone can mathematically justify the optimal number.
I think Roger's thoughts are very pertinent – there are large number of WTS/WTB posts, but an even more huge number of viewers. If you don't get a bite, maybe the best idea is to abandon the fishing hole, or else come back and try again somewhere down the line to hit a whole different set of fish… er…people. Also, many, many sites have a no-bump rule, and while it can be debated how important it is to enforce this, depending on the circumstance, don't be so provincial as to suggests that this is something that just came out of thin air. If I was R I'd probably be damn tired of explaining things to all the people who "know" a much better way.
Also, and I think this is important, this is not EBAY. Facilitating your sale should not even be on the top ten list of relevant worries here, IMHO. There are too many more important issues to the site as a whole. If you don't like it you have many other options on how to buy and sell stuff. Personally I have always REALLY wished there was an option setting to put the classified stuff in the same category with chaff – invisible in the "New Threads" list. I (and I assume a lot of people) almost never want to see those mixed in with the "new threads", and when a real new thread is only every tenth posting the SNR will be too low to bother coming to this site except to buy and sell stuff. Likewise I'm sure the people who mostly (at a particular moment) want to buy and sell would be happy to have the new items in the classifieds isolated as well.
On some sites the rules say you are supposed to delete the whole thread once a sale is concluded or abandoned – not just write "SOLD" in there. That helps keep things cleaned up a bit. I know there have been numerous debates over that and related issues on here – some people like to look up the price of a similar previously sold item to judge what the "market rate" might be, while others feel this information just decreases the SNR.
Some sites have the "advanced" web feature of outlining all the posts in a forum that have appeared since the viewers last visit. That can help quite a bit for those obsessed by the classifieds – or other parts of a site. Having threads in the classifieds auto-delete after a certain amount of time, and/or after a certain amount of no activity would be a great idea to go together with a hard rule on no bumps. Lots of potentially good ways to manage things when the SNR starts to go down as the traffic goes up. But I've been on here too long to expect the BPL web software to ever change or improve. The good news is that if we go another decade or so it may be considered "quaint" or "retro" instead of just backward. Things go in cycles.