I think there's two main issues you're addressing here:
1. Doing face-to-face missions.
2. Missing church to do missions.
Concerning mission, I think the western Church in general needs to rethink how we define missions . . . and I think that this redefinition is happening now to some extent.
For too long, the Church has thought of missions either as going somewhere several hours or hundreds of miles away from our home, to tell the gospels to other individuals AND/OR missions involved writing a check, or collecting soup cans or coats at the church in order to distribute them to those in need (an extension of this view is holding a conference, small group or class at the church and inviting people in the community to come). Now, both of these things are legitimate, but I think a key component is missing . . . the church needs to do face-to-face missions in their own town . . . not by expecting people in the community to come to their church, but by going out into the community and building relationships with people who would never come to a church. (For example, my church just held two weekends' worth of free oil changes for single parents at a local auto repair shop, and in previous months we've rebuilt roofs, painted houses, raked lawns, etc..) I think the church too often gets complacent and expects the community to come to them, instead of going into the community. And in all honesty . . . it is very hard to go into the community to help others face-to-face; not because it's hard to help, but because it's hard to find opportunities to serve, and there's usually a lot more closed doors than opened ones.
As far as number 2: There's nothing wrong with missing church every now and then. But there has been a trend in the last few years of churches shutting down their building on Sunday mornings in order to "be the church" in the community and do service-projects on Sunday mornings. The problem with this, as I see it, is that it neglects the need and essential importance of biblical preaching. Preaching and listening to preaching is THE single most important function of the church. Period. I can go into all the biblical arguments for that assertion if you'd like, but for now, the notion of a church shutting its doors on a Sunday morning to "be the church" in the community, isn't "being the church" unless biblical preaching is being done in another location.
Again, I don't think there's any problem with missing church from time to time (especially to share the gospel with folks), but there will always be tension in the area of skipping a Sunday to "do ministry" when the preaching of the gospel is either missed or neglected.
As a pastor I would not sanction a program that took people away from biblical incarnational preaching (and by incarnational, I mean "in the flesh"). But in the same regard, I would be thrilled if I had a member (or a handful of members) who came and talked to me and told me about a mission like the one you're doing and asked me if it would be okay to miss church once every other month to share Jesus with bikers. And of course they would have my enthusiastic blessing!
I'm glad you're doing what you're doing and see your mission field is right in your own backyard.