I wouldn't do it solely for the purpose of improved technical quality with 11x14 and 16x20 prints. I don't think you'll notice any difference at all between 4x5 and 8x10 at those print sizes. If you wanted to contact print, or make really big prints, or use an alt process or just thought you'd enjoy tusing 8x10 that might be different but for an improvement in print quality at the print sizes you mention, I don't think you'd see it.
I've owned three 8x10 cameras at different times in the last six years so clearly I've vacillated a lot about that format. The problem was that I really enjoyed using 8x10. I found it such a pleasure to compose with the 8x10 ground glass and I just liked handling the the bigger film, bigger negative holders, etc. But in the end (at least I hope the last 8x10 was the end) I decided that the ability to make contact prints (which was one of my main reasons for getting into 8x10 in the first place) plus the pleasure of use weren't worth the difficulty of carrying it around. Also, I think my range of subject matter was narrowed because I couldn't get it to difficult places and because of the shorter range of focal length lenses that I could use with 8x10. With 4x5 I often use a 300mm lens but that's a 600mm lens in 8x10 and dealing with a bellows extension of 24+ inches isn't easy. So with 8x10 I found myself photographing scenes that lent themselves to shorter lenses and my photographs seemed to have a certain sameness about them that isn't present with smaller formats.
But like they say, you only go around once, this isn't a dress rehearsal, etc. etc. If you think you might like it give it a try. If you buy good equipment used you should be able to sell it for what you paid for it.
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