I have previously mentioned that games with achievements have better sales and ratings, which is to say that you can both make more money and increase the average user’s enjoyment of your game by incorporating achievements. That’s a significant win-win for tossing in some decorative trophies.
If your game does not have achievements in it, you are probably leaving money on the table. While business acumen and game design are not entirely overlapping areas, and some people take a principled stance against achievements, I worry about the quality of the product you are selling if you are overlooking proven methods of improving both your sales and the perception of your product. Bad decisions are correlated with other bad decisions.
This has become a signal I use when shopping on Steam. It is not an overwhelming factor, but it has helped avoid some marginal purchases. It is a signalling game: whether or not you like achievements, their presence or absence potentially says something. Unless you are explicitly counter-signalling by pointing out the lack of achievements (the way Magicka points out its lack of side quests), I’ll tend to assume the worst. Not caring in one area can be correlated with not caring about others. Maybe adding achievements is harder than I think, but how many copies of indie games sell when Steam has its semi-annual raffles and awards tickets based on achievements?
Basically, I am asking the game to say, “shibboleth.” Know that this will be used elsewhere in your life. If your cover letter or resume has the keywords that indicate that you are “one of us,” you are more likely to get an interview. If you fail to observe the server’s conventions in your LFG message, you are less likely to be invited to group. Fly the colors if you want to connect to your tribe.