Sorry for not following up on this sooner! I just got an email from JIRA about this on some updated comments, and it looks like it's been marked resolved as of December.
Anyway, I'm happy to report that that database size has remained relatively small over the past few months. We've got 115,000 items in our contentstore folder totalling 22 GB and the database size is just over 1 GB. The alf_prop_value and alf_prop_serializable_value tables are very small, 152 KB and 32 KB, respectively.
The largest tables are alf_node (387 MB) and alf_node_properties (342 MB), alf_child_assoc (115 MB), alf_transaction (60 MB), alf_node_aspects (55 MB), alf_content_url (45 MB), and alf_content_data (38 MB). All the other tables are a few hundred KB or less. I assume this is normal.
Since the original post, we've upgraded to the 201512 EA release, the 201602, 201604, and 201605 General Releases, and we are now using the the 201606 EA Early Access release. Everything seems to working well. Aside from the occasional transformation failure, the log files are clean and our users haven't reported any problems.
Thanks again for your help, and thanks to the Alfresco developers for putting together a great product!