There is a difference between "wanting reforms" and "reformism." Liberals are reformists by definition, not revolutionaries. The liberal position holds that the basic structures and institutions of our society, representative government and capitalism, are flawed and we must alter them to make them more just and equitable. Reform is the goal, and this is the defining feature of reformism.
For those radical leftists who ultimately want something more, reform cannot be the goal. That doesn't mean, however, that we can't seek reforms in the short term. Ending the Iraq War, for example, is only a reform. It doesn't challenge war and militarism itself, but it is something that radical leftists desire. There is a long history of a "minimum program" that leftists have sought, which is on the surface not all that different from what the more progressive liberal seek. The difference is that leftists see this program as a stopgap measure to be sought concurrently with a "maximum program" of revolutionary change.
This difference between reformist liberals and revolutionary radicals is why leftists should avoid participating directly in electoral party politics by forming parties and running candidates. Working within the system accepts the limitations of that system. That isn't to say that radicals should not vote for candidates who support their vision of a minimum program, but they should never run candidates or form parties built around that program. Every time such a tactic has been tried, most catastrophically with the German Greens, it inevitably results in the "radical party" becoming indistinguishable from the reformist liberal parties already in existence. When you are focusing on winning campaigns rather than making changes, you have to appeal to broad audiences. Your focus is on taking power rather than dismantling it. This is no strong criticism of the individuals involved, it is just the price of participating in the system.
The solution to the paradox of achieving reforms without becoming a reformist is to achieve them not from inside, but from outside. Putting political pressure on those who are already or will be in power (indeed, threatening them in nonviolent but meaningful ways) to reform is the revolutionary method of achieving them. This ranges from mass demonstrations to civil disobedience to, yes, participating in elections. Doing all of these extra-systemic activities allows the revolutionary to build solidarity and movement cohesion, to improve people's lives in the present, while agitating for meaningful change in the future.
Ultimately, the goals of reform to a revolutionary are threefold.
First, reforms should help people who need help now. Racism, sexism, homophobia, and economic inequality are real and present, and to ignore them now while hoping to solve them after the revolution tells the people who are suffering their effects in the present that the Left doesn't give a shit about them. If we want a movement to grow, we have to offer those who would benefit most from the movement a chance to improve their lives without mere promises of utopia.
Second, reforms should be educational. This is especially relevant during an election cycle, when people are paying slightly more than their usual zero attention to politics. There are many people who do not even recognize that there is a problem, much less think anything can be done about it. Calling for a minimum living wage (while being explicit that it is necessary because capitalism is unjust), for example, keeps attention on issues that we face, rather than on the soma of comfortable consumerist middle class life. Reforms must always aim to increase tension between the people and their rulers.
Finally, reforms have a value simply by giving people hope. If our only goals require mass consciousness, and mass insurrection, and we face the prospect of spending our entire lives never seeing those goals realize, it is no surprise that many radical youth simply grow up and give up. Winning small changes in the system that are aligned with the values we support gives a sense of progress to a movement that faces enormous obstacles. Yes, the sense of progress is illusory, but it is a functional placebo, keeping spirits high and reminding us that change is possible.
Ultimately, we need mass involvement of people in the struggle for liberation. Until we have a majority of people on our side, though, we need to put as much pressure on those in control of our collective destiny as possible, through all the means at our disposal.