How to resolve RESOURCE_SEMAPHORE and RESOURCE_SEMAPHORE_QUERY_COMPILE wait types

We are trying to figure out root cause of slow running sql server queries hitting/fetching data from one of the database , size 300 GB, hosted on server with below configuration:

Windows server 2003 R2, SP2, Enterprise Edition, 16 GB RAM , 12 CPU'S 32 Bit

SQL server 2005, SP4, Enterprise Edition, 32 Bit.

We have already informed business on the upgrade to 64 bit which would take over a month.

But for the current issue, we are trying to gather the data if we can resolve the memory pressure or finally come to a conclusion to increase RAM.

Action Completed: Re-indexing and update stats are proper for this DB.

As shown below, we have been noticing the semaphore waittype for past 5 days, ran during the load hours:

Few info after below queries: size of buffer= 137272

SELECT SUM(virtual_memory_committed_kb)
FROM sys.dm_os_memory_clerks
WHERE type='MEMORYCLERK_SQLBUFFERPOOL'

and semaphore memory= 644024 per below query

 SELECT SUM(total_memory_kb)
FROM sys.dm_exec_query_resource_semaphores

Below is some more info gathered from dm_exec_query_resource_semaphores and sys.dm_exec_query_memory_grants dmv's

So from above info gathered and per SP_Blitz data Resource semaphore seems to be the problem.

Is memory 'target_memory_kb' assigned for resource semaphore id's too low, as compared to 16 GB RAM available.

Note* per analysis on 8 hours run 'target_memory_kb' is always under 1 GB, compared to 16 GB available?

what could be the issue here and how to resolve, please suggest

Thanks