Should we limit our tech partnerships?

First, here's why your agency should partner with as many tech companies as you have in your client services and internal stack (at least):

1. Increased exposure and thought leadership - You are already vetting tools and choosing to use them... Why not allow those tools to showcase you to their audiences (partner directory profile, webinars, events, case studies, expert tips blogs...)? 
2. Increased support - You need your clients to come to you when they need support right? If you are not a partner of that tech, you will not have the increased support a partner would have and therefore are not supplying your clients with adequate support.
3. Leads - The best services you can offer clients are the one's you do often. If you do them often, you use the same tools. If you are partnered with those tools, and their sales team (or customer success teams) knows you are selling stable services on top of their product, they will be more inclined to refer you their users.
4. First to know - Your clients rely on you to be ahead of large releases, new integrations coming, feature depreciation... As a partner, you are included (most of the time) in the product roadmap and are filled in way ahead of any big changes.