With respect, your post above is clear indication that you do not understand the CPU and RAM usage load scripts like WordPress can place on a server, even with few visitors. The overwhelming majority of sites with CPU/RAM usage issues on DreamHost's shared hosts are pre-3.0 WordPress sites that are poorly implemented and cluttered with CPU intensive or poorly written (or both) plugins.
These sites can, and do, crash and fail with far less than 60 visitors a day, and I have seen them fail to load a single user at a time without exceeding the RAM limitations necessary on a shared server.
We are constantly having to explain this to WordPress users who "just don't get it" because they do not have the necessary technical understanding of how WordPress works and how it use RAM.
What you do with your sites, and how you plan to monetize your sites or pay for your hosting is your decision to make, but our need to keep our shared servers stable and responsive has led us to preclude the use of WildCard DNS on our servers. This could change, at some point, as everything is subject to change, but such a change is not anticipated in the near future.
There are those running WordPress MU right now on DreamHost's shared servers, using sub-directories instead of sub-domains, and this is allowed as long as the site does not overload the server, but if you want to have WildCard DNS implemented, that is only available to DreamHost customers on DreamHost PS (VPS) servers.
We are still working out how we will accommodate WP 3.0 users using MU mode on shared servers, and there may be a special hosting plan for that at some time, but for now you can install it on a shared server and run it using sub-directories if you have the expertise to do so and your installation does not negatively impact the operation of the shared server.
Support for this installation is not available from DreamHost support staff, however, and if you do this and create a resource problem on the server, our admins will intervene and you will be required to remove the installation or migrate it to a VPS server (or to another host).