Keep spare LED bulbs or increase dimming?
I don't have a good solution for you, I'm afraid, for the lamps you've got. The majority of LED lamps are a lot more complex than the simple incandescent lamps of yesteryear.



Figure 1. Phase-angle dimming control. Source: Dimmers for LEDs.

Depending on the internal circuitry of the lamps they behave differently to the short pulses of current around the switching point. Any lamps with built-in smoothing capacitors, for example will store the peak voltage and may not show much difference in adjustment between max and 50% settings. Variations in component tolerances - and there will be many as lamp manufacture is a very price sensitive business - will cause variations in response to the applied voltage. The LEDs themselves will have variation in VF, their forward voltage, from batch to batch.



Figure 2. The capacitor, C2, messes up the response of the lamp on a phase-angle type dimmer.



Figure 3. A possible solution. LED filament lamps

LED filament lamps, if available for your lighting fixture, may offer a good solution. These are WYSIWYG (what-you-see-is-what-you-get) in that there is generally no tricky electronics to deal with and the lamps behave reasonably well with dimmers. I only have one at home and its on a dimmer. For some reason, which I must investigate, it gives a brief pulse of light on switch-on of the dimmer but works normally thereafter. These lamps are aesthetically pleasing too. Check the colour temperature of the lamp you choose as many are deliberately warm to mimic the incandescent and, as is often the case, the warmth may be overdone to make sure the consumer feels s/he is getting good value!

I have written a little more on the topic in the articles linked above.