Thanks for all the good comments, brothers and sisters. This is a critical topic, and I've continued to think about it, especially with reference to my own hesitancy to encourage vocations and what it might be about.
Perhaps another reason why I find it challenging to encourage vocations is that, in my experience, I feel like we promote the common religious life wrongly. Though this was completely alien to my own discernment, for many men who discern there is a choice to be made between the secular priesthood and religious life (including, perhaps, the religious priesthood.) Within this dilemma I think that we sometimes set up an unhelpful distinction between a caricature of the secular priesthood as lonely, solitary, and unsupported and the common religious life as one in which you can depend on mutual care and support. To me this is very dangerous.
It's true that the common observance can provide a kind of safety net from spiritual ruin. Even when you can't pray and don't want anything to do with spiritual effort, you still have an obligation to common prayer and the common table. Somebody might notice if you totally disappear. These are both good things. On the other hand, though, if someone enters religious life in order to fulfill his needs for friendship, support, or (to use some of the favorite words of those who try to sell us this bill of goods) mutuality and intimacy, he is going to be disappointed.
If we try to encourage vocations to religious life by convincing people that it will serve their own emotional needs, their vocations will end in disaster. Yes, a brother will make friends in the community, and this will be an invaluable support in the life of observance and ministry. But this is not the primary purpose of the common life, which is provide--as St. Benedict put it--a "school for the Lord's service." The common life at its heart is meant to be a penance in the best sense of the word, an opportunity to do violence to ourselves and bend our minds and wills to God.
The common, religious life is observed not to serve my emotional needs, but to give me a chance to discard the emotional tyrant that I have come (falsely) to regard as "myself."