I'd point out that just because they don't have much logging doesn't mean that they don't have any. Assuming you recognized the intrusion before the log rolled over, I believe that you would see evidence of it on most of the consumer-grade SOHO routers I've used if logging was enabled. I was able to detect intrusion (and DoS) attempts on routers from DLink, Linksys, and Netgear by analyzing their logs relatively near the event.
Additionally, if you were looking to protect a deployment, running dd-wrt provides a significantly much more robust logging mechanism through syslogd that supports logs being offloaded to provide a permanent record and avoid the rollover problem.
However, as I believe was pointed out above, logging is often off by default on these devices and as a result I can't see being able to get much from them in that case.