OBIEE 10g doesn't have the concept of Simple / Enterprise installs as such, this was new in 11g.
You can scale out an OBIEE 10g installation to make it a cluster but it's a manual task. There's plenty of stuff on the web about it though.
Do you know for sure that your performance issue is caused by lack of OBIEE server resource?
In one of the site where I was working, there were many reports getting failed and the client have raised an SR with Oracle regarding the issue. On their analysis, they have mentioned the same as below.
Also you mentioned that you deployed the analytics, bioffice and xmlpserver on the admin server , and you do not mention any managed server so it sounds like this is a Simple install (and not an enterprise one).
Please note that the Simple Install type deploys all selected applications to a single WebLogic Server instance and is ideally suited for demonstration, evaluation, and proof-of-concept purposes, because you cannot scale out if needed
Since I am not in site currently, I couldn't get the exact reason of the error. So, I raised this discussion.
If you are using OBIEE10g then the above concept/reply from Oracle technical team is not for you. As rmoff said you can scale out obiee 10g with manual intervention.
When you said reports getting failed, do you know the exact reason for this? Do you have any logs which you can share?
Currently I don't have access to the Client system or log files to share with you unfortunately. Let me share with you once I receive them.