turning on super-nitpicky writer mode

• "Many of us come from different online communities, either as established artists or growing enthusiasts [this sounds strange, but I can't think of an alternative]. All of us are people with a serious interest in this piece of software that we have grown to love."
• "Bryce fills [<--present tense! Bryce is not obsolete! It's a subtle change, but things like that can stick in the subconscious.] a void as a mid-level and affordable rendering solution for both the weekend warrior as well as the dedicated professional who use it not only for landscaping but also a variety of other fields. Indeed..." [maybe leave the part about uses out or put it in another paragraph - you're talking about the people in this paragraph]
• cannot is one word
• "Its basis is as stable as the undersigned..." not sure what this means. Are you talking about a stable user base?
• "All our appeals to Corel, all our pleas to continue the development of Bryce--which is by no means obsolete ["or past it's time" is redundant]--have largely failed [no comma] due to Corel's shaky financial situation"
• "direction in which it plans to take the development of Bryce, whether that be continuing it or selling it to other parties...."
• "not after so much work has been put in it and such a large, dynamic community has been built upon it...."
• I agree about "only"
• "We sincerely hope for [or perhaps "anxiously await"] a reply from Vector acknowledging the receipt of this petition." [this sentence seems a bit tacky, but I don't know, it might help....]

Feel free to ignore any or all of the above suggestions. I've been told I'm a good writer, but I'm far from a professional; hopefully someone else will know better than I do. The content itself of the letter seems good to me, I can't think of anything to add.