The occupy mobilization is just that, a mobilization. It was never a thing organized enough to be co-opted. It was blank slate that anyone was able to put their imprint on. The advantages and disadvantages to this have been well documented and I won't go into them here. I will just comment on the Dems and GOP. Political Parties are, in the U.S. reflections of a combination of varying factions of business interests. These varying factions form voting alliances with voters along mostly market and brand psychology oriented techniques. In other words there is nothing inherent in an alliance between a Hollywood mogul and a Dem voting soccer mom, and an alliance between the CEO of Raytheon and a GOP voter. Both are an alliance between a top and a bottom. A financier who controls the party at the top, and a voter who buys into the brand at the bottom. It's all advertising, and both parties are built around this and it makes it impossible for people at the bottom to form a common interest based along class lines.
The Dems happen to be associated with the branding of the old left/liberal alliance of the 30s-70s. The Liberals were almost certainly in charge, and the left in the U.S. never had any footing, even under this coalition, though it was obviously much stronger than it has been from 1980-2012. Liberals are primarily overloaded in the top 20% of the economy, most have college degrees. They derive income/power very differently from capitalists, but they are also very much empowered in ways that working class jobs are not. There were once Liberal Republicans and Democrats. But the politics of the 1960s created an overloading within the Democratic Party of the Liberals. By the end of the 70s, it would be clear that the Liberals would dominate the Party, at the expense of the left, despite the fact that the working class dwarfs the liberals in size (which explains why the Dems have such a hard time defeating a conservative coalition that rarely pulls more than 25% of the eligible electorate).
The problem with this should be obvious, but if it is not, it is that a serious political democracy would allow majority populations to have a dominant say over resource allocation. Our system ensure that resource allocation is private, and people get to vote on mostly frivolous things, though there are some legitimate issues tucked away within. But for the most part, if you pick any 2 random spots on the bottom 80% of the triangle, and these votes will never be able to vote along economic lines, but will often cancel each other out.
People who don't want occupy to get co-opted need to recognize that there is nothing to be co-opted. It's a shell. If you want to build something that can be co-opted in a more serious way (ha ha) we must have a stronger program that advances a more serious agenda (i.e. abolish the senate, expand the house, limit the executive branch, provide a guaranteed income for all, etc) Then it won't matter if the Dems jump in and try to take it over, because you will be able to force out those within the Party who are unwilling to part with their support for elite interests.