What Bob said. Either replace the entire filter setup with one you like or stick with what came on it. As for the sediment bowl I would upgrade that to a glass bowl because it makes maintenance easier. You will still want a sediment bowl no matter what secondary filter you use.
If you are not seeing that much material in the sediment bowl, it is a good bet your tank is in decent shape. As long as you make sure another infection doesn't get started you should be good there.
How often are you replacing the spin on secondary filter? What filter are you using? If you are replacing it fairly often and still getting a lot of crud in the injection pump maybe you should change brands of filters. I have numbers for WIX, NAPA (made by WIX) Fram and AC Delco. I am sure there are others.
Whatever you are finding in the IP is WAY bigger than even the largest spin on filter, indicating there is something else going on. Replacing the OEM housing with something else is not likely to solve your problem until you find out what the problem is.
IMHO there is nothing wrong with the OEM setup as long as you use a quality spin on filter. After all it is just a housing with inlet and outlet, the filter does the work unless if fails. IF you want to have a visible bowl at the secondary with a drain on it, that is fine, but it won't solve your problem just by installing it. Besides, the sediment bowl gives you the visual check you are looking for, just a little farther upstream.
