I am glad that you were able to rectify your GMail issue. For what it is worth, one of the advantages of having Android 2.2 and up is that you get fast updates to the GMail app because it is available for download in the Google Play Store.
As for Dalvik cache, it is basically the code of your apps compiled into bytecode, which is much easier and more efficient for your CPU to process quickly. So, all wiping Dalvik cache does is clear that out, but it immediately gets rebuilt when you reboot and subsequently use your apps. This is also why the first boot after flashing a new ROM takes a bit longer than normal. Your Dalvik cache can be wiped with no ill effects, and if you feel something is not working correctly or your handset just feels sluggish, give it a try.
Nokia 638 > Motorola Talkabout > Motorola V60t > Motorola V60i > Motorola V505 > Samsung Epix > HTC Hero
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