I have used screw-on close-up lenses (a.k.a. filters) since the '70s. I have two sets, one for 49mm and one for 52mm. Each set has a +1, +2, and +4. They are convenient and don't reduce the amount of light reaching the sensor by any significant amount if you only use one or two at a time. I usually only use one at a time; I have very seldom stacked them. Yes, you can combine a +1 and a +2 to get +3, but I have not found this to be necessary to get the framing I want. YMMV.
Of course, any time you add more glass to the light path, you are going to degrade the image somewhat. However, since the close-up lenses magnify details within the image, this fine detail is spread over a larger portion of the frame, and captured by more pixels. Though adding more glass may technically reduce lens resolution, the net affect is that the added magnification makes this less important in capturing detail.
Consider these screw-on close-up lenses as lenses indeed, and buy the best quality you can afford. I haven't researched them lately, but I'm sure there is a variety of prices and quality levels out there. Uncoated, single coated, multi-coated, etc. A high quality close-up lens used with a high quality main lens can give pretty good results. Not as good as a dedicated macro lens, but 1/10th(?) the price.
Pentax-M 50mmf1.7 with +2 Vivitar close-up lens
Pentax-M 50mmf1.7 with +1 Vivitar close-up lens