It is required for downloading support packages (using maintenance optimizer). I think this requirement has been since April 2007.
You need Solution Manager for Maintenance Optimizer, which was made a hard requirement as I understand for SolMgr Enterprise version. It is also required to do upgrades to releases prior to ECC 6.0 to request and assign the serial numbers.
That being said, there are plenty of examples where customers have installed SolMgr simply to get their upgrade keys and then tried to walk-away from SolMgr.
If you want to change minds, you need to think about how you really want to utilize SolMgr and the variety of capabilities that it has. At a minimum, you want it/need it for all of the performance metrics collection and submissions to SAP for the EWA reporting and analysis.
You "can" use it for documenting all of your business processes (with business detail), or you can simply use it as a place to attach your technical documents. You "can" use it for defining enhancement projects, upgrade projects, and other maintenance projects. You "can" also use it for integrating ChARM into the various modules so that you don't need an external trouble-ticketing/routing software tool.
In the end, you need to define what you want to use it for. From what I've seen or heard at different Webinars/seminars/Sapphire it
can be anything and everything. SAP tells you that it will do a lot of things -- maybe not in a best of breed approach, but certainly at the most cost effective model since once you own it, whatever you use is still free. The other best-in-breed tools will cost you more but you'll likely get what you pay for with good planning.
Exxon-Mobil did a nice presentation of their SolMgr environment at this year's Sapphire conference. Primarily as an IT documentation tool, with some external business users accessing the documentation as well. We may take a very similar approach as we are just now embarking on bringing up the latest environment in DEV and PROD.
In my understanding, the components/best practices from SAP that need to be implemented are:
1. Install and use Solution Manager Enterprise Edition - 7.0 EHP1.
2. Connect to SAP OSS thru solution manager
3. Document your landscape in solution manager
4. Activate EWA (Early Watch Alert) and
5. Install and configure SMD (Solution Manager Diagnostics) for those on ECC 5.0 and above
The Enterprise Support requirements for Solution Manager are spelled out in the Enterprise Support scope definition at http://service.sap.com/enterprisesupport. The Solution Manager requirements are not all grouped together in that document, however, so I published an article in the first edition of Solution Manager Expert last October summarizing those requirements: http://www.solutionmanagerexpert.com/article.cfm?session=7a95b16e-83cd-457b-bb5c-2724f6e8adca&uid=9e394294-f291-428b-b022-d0f34466c2a3. (This requires a subscription to Solution Manager Expert.)
The SAP scope definition may have changed since I published my article, so I would read the article first, then review the SAP website regularly to catch any deltas.