I think it depends on what you would use this other pair of binoculars for: more reach/magnification or brighter view at darker hours?
If the main use will be during the day, with good/OK light, I think you might not gain anything significant from a 8x42 compared to your 8x30 (both of comparable quality optics) if you already like your 8x30. If it is aimed as an alternative in open field/coast location, on the condition of having steady hands/holding technique and/or e.g.some support (e.g.leaning on something), than the 10x does add a bit of detail/magnification.
If you like your 8x30 and (almost) never miss some added brightness but only reach, I would probably go for the 10x42.
My personal experience is as follows: I have had a good Kite Birder 10,5x44 for >15years now as my only binoculars and bought a Kite Lynx HD 8x30 a few months ago. I’m now almost always using the 8x30 and take it with me more often than I did my 10,5x44 (also on smaller walks with family not aimed at observing) as it is so comfortable to use (considerably lighter,,compact enough but not too much,thus easy to hold,8x thus a bit steadier,wider FOV and easier for friends/family to use when walking together). I will keep my 10,5x44 both for sentimental reasons (my first own and until last year only binoculars) but also when going specifically to coastal areas/open field/observation posts or in much poorer light (very early/late,e.g. owls or so, even though a 50mm,which I don’t have, would probably be better).
I have to admit that I’m not sure which option to buy myself in a future upgrade, considering my current setup. I bought my first spotting scope end of last year and find it to make a good tandem with the Lynx 8x30. Thus maybe I should stop the big spendings...
If you don’t own a spotting scope or plan to some day, I would recommend to test how steady you feel with the heavier 42mm and 10x. If OK and you feel a gain in details observed compared to your 8x, I would go for the 10x42mm.
There is also the option of a 10x50, like the relatively(for a 50mm!) light/compact 10x50mm Kite Lynx HD of course...

. I have never tried it though, so I cannot comment on it, but I would probably consider it as a good 2-binoculars-setup: a 8x30/32 + a 10x50 , but would try it first. (while for a single-binocular-setup I would go for 8x32 or 8x42...)