Rhys, you're of course not alone in wanting the LP to become a viable force for moving public policy in a libertarian direction. In fact, nearly all Libertarians want that. Some of us are online here: http://reformthelp.org
I agree completely with your motives and goals, so (in typical Libertarian fashion) I'll only write about a few disagreements about strategy and tactics.
1) You say Ed Clark's presidential candidacy turned you into a Libertarian, and then you say we shouldn't run presidential candidates. I want more people like you in the LP, so I favor running more Ed Clarks for president.
2) I can't agree that the LP is perceived as being part of the "religious" right. Our positions have been consistently pro-choice and pro- personal freedom, and I'm pretty sure the LP has never invoked any deities in its publications or national meetings.
3) Libertarian campaign resources aren't really fungible in the way you seem to think they are. Nearly all LP campaigns are self-financed by our candidates, and there isn't much hope in getting our candidates to stand down en masse and focus their resources on a few races. However, there is an LP organization that seeks to focus LP contributions in a similar way: http://www.lncc.org/. I hope that all Libertarians who favor your strategy will donate generously to this effort.
4) I agree that being a swing minority voting bloc in a legislature could help us move public policy. I think the same is true for being a swing voting bloc in elections themselves. I agree with a strategy of not opposing a major-party candidate when 1) he is sufficiently better than his major-party opponent and 2) the absence of LP opposition could plausibly tip the race to him. The Republican poster child here would obviously be Ron Paul. Who would you say is the Democrat poster child?
5) I agree that now is a great time to weaken the Republican Party and recruit from the debris, but we must do so in a way that doesn't make us seem more conservative/Right. Our branding must always say that we are the only choice that is neither Left nor Right, neither liberal nor conservative.
6) Deference to the LP's anarchists prevents the LP itself from officially saying very much in response to your excellent questions about the purpose of the State, how to reform taxes, etc. However, our Platform now gives room to both minarchist and anarchist candidates to offer their own best answers to your questions. My favorite answers are to promote 1) a strict interpretation of the Constitution and 2) a Green Tax Shift: http://knowinghumans.net/2008/01/tax-bads-and-untax-goods-with-green-tax.html