Bonus Mission Pack was (in a lot of ways) a prequel. Do you own it?
They don't have resources in GW1 for something like that to begin with, but even if they did it would fail hard for several reasons:
1) Size matters. People don't like a few bonus missions that they blast through in a few hours; they want a campaign. That's well beyond the scope here.
2) Replayability. A few bonus missions provide very little playability unless there is a huge reason to replay them...like fat, fat loot. That leads to problem #3.
3) Let's say they add a dungeon pack that includes two awesome dungeons where the ectoplasm, obby shards, and torment gemstones flows like rain...for only $10. Cue whining. People will whine that the new area gives people an advantage for money. Other people will bemoan the loss of activity in the UW, DoA, and FoW.
4) Profit. Think about the effort that went into making the BMP for $10. Now think about the fact that people (like myself) are willing to pay money for extra character slots, costumes, mercenary heroes, etc. We're not being charged monthly for GW1, and they aren't making money on GW2 yet, so as a business I'd probably be doing the same thing. I've been very happy with how ANet has handled things and maintained equal advantage for all players to the extent that they have.
I'd highly encourage you to check out the BMP if you hadn't, and I'm not sure where you are with your titles, but doing those in HM have added
tons of replayabililty for me. I almost quit GW two years ago because I was so bored after finishing the campaigns and having nothing to do. Now if they'll just add another overarching title for super-HM...
Edit to add: I also thought game time was going to be doomed after having a child. Just not so, they sleep a lot. As said, don't expect to play for 15 hours straight very often, but a few hours here and there is no problem. Let me also say:
THIS IS WHY I LOVE GUILDWARS SO MUCH THAT I TYPE IN ALL CAPS AND BOLD.
I do not believe I could play WoW or other online games that require coordination of teams. GW is the right game for my schedule.