I am looking at steam injection for my newly insulated keg mash and liquor tuns. After a normal single infusion brew I can see my temperature loss in my equipment and see if I even need it or not. I am building a stirrer so I shouldn't have to open my lid to release any heat from the mash tun. If you are having temperature loss in your tuns maybe the lids are being opened too much, or the lids aren't insulated for heat (but cold) so you may need to blow foam insulation into them. I know some of the cheaper ones are simply hollow plastic and a drill and some great stuff foam work great.
I try to keep the ports on my tuns and kettle to a minimum so I use the same ports for everything. I fill my mash tun from the bottom with gravity and stir. If you are doing infusions for stepping this helps because your hotter temperature water is trying to heat up-wards and with stirring helps to heat the mash faster and more evenly. Adding water through the bottom also helps with stuck sparges. I am planning on starting with the newly beefed up insulation tuns and then have the ability to go directly to steam infusion if needed later. Regardless, I won't have to have any extra valves or other stuff. My theory on mash tuns is to add your grain and water, then have it so it is shut the whole time. I am incorporating a ice cream mixer into the lid of mine so it should never be open except to take decoction fractions if ever needed for that style of brewing. Something to think about, but I think with your equipment you have a couple of options for improvement over starting over. I don't use them because my system is older than the idea coolers. They work great as HLT and MT, and with the other information on this forum about temperature controlled HLT and stuff you should be able to get a great idea and sculpt your brewery into your needs.