We recently bought a house built in 1976. The property is relatively rural but does get city water. The water pressure in the whole house is less than desirable, so we had a plumber come out to tell us what was going on. In addition to two clogged water filters (which we replaced,) this valve was installed between the main and the filters, so he removed it altogether. None of these "repairs" seems to have affected the water pressure for better or worse. So my question is, would my water pressure improve if I installed a valve downstream of the filters? The water is very hard and has lots of sediment, so I can't realistically remove the filters. What else could possibly improve the pressure otherwise? All of the faucet screens, etc. have been cleaned...
The first thing you should do it check your static (no flow) water pressure and the pressure with water flowing. Find a place where you can attach a pressure gauge and check the pressure with and without flow. You need to find out if this is truly a pressure issue or if the issue is related to restricted flow.
Check the static and flow pressure both upstream and downstream of the filter units. Looking at the pressure drop while water is flowing should tell you if the issue is restriction.
1) the valve he removed is a pressure regulator; regulators are usually installed for a reason (to protect pipes and fixtures from high pressure), if your upstream static pressure is higher than 85 psi (or if your neighbors tell you there are issues with pressure spikes) you should have a regulator.
2) the "set" pressure listed on your old regulator was 45psi, that is pretty low. I would adjust your regulator to no lower than 65psi, no higher than 85psi. The fact that removal of the regulator did not improve conditions makes me think you have a different problem.
3) filters restrict, that is how most work. Chemical filters restrict flow too because they need "residence time" contact between the flowing water and filter media.