There are a wide variety of reactions on the price of the level 90 character boost. Was interested in collecting some data in the form of a poll in regard to the price, as well as people's thoughts on this matter.
Personally, I think the price is fair, considering it is an option, and people still have the choice to spend the time to level a character the traditional way to 90.
A character boost will allow those veteran raiders who have quit the game an opportunity to come back to the game and level up with their friends, with less of a barrier. This will allow those people who have full time jobs the option to save a lot of grind time and provide them with an avenue to quickly catch up with long-time players. The price also acts as a deterrent for people to purchase multiple level 90s without a second thought, and forces people to be a little more conservative with which character they should boost, and how many characters they choose to boost (unless people are willing/able to spend a few hundred dollars on multiple lvl 90 characters)
I've read arguments that this will "ruin the game" and "flood the game with people who don't know how to play a class" etc. I only see this having a real impact on PUG groups, and LFR. For the veteran players, and raiding community, I foresee little impact. Raiding Guilds generally recruit based on player skill, and are more selective on who they bring into their raids.
If it is apparent that people do not know how to play their class, they do not get a raid spot. I see plenty of players that have leveled their way to 90, that still do not know how to play. Those people are removed from the raid, and thus have little impact on my gameplay experience.
TLDR: I do not see how the option of purchasing a level 90 will have any substantial impact on the gameplay experience of Raiders and skilled players.