If we turn out and vote, the Democrats have a good shot at winning the House and a very slim chance to win the Senate.

This won't result in the Democrats stopping the Republicans' legislative strategy, because they literally have none.

It won't result in Democrats passing legislation, because Trump will veto any bill that passes and the Democrats won't be able to get the two-thirds majorities to override.

It won't mean that Trump will be impeached, because the Democrats won't be able to get 67 votes in the Senate. Not a chance in hell that will happen, no matter WHAT Trump did or does.

So who cares? Why vote?

Because of what it will mean to Trump's reelection chances to have all the House committees and the power to serve subpoenas and hold public hearings. If the Democrats win the House, they will:

Use their chairmanship of the tax committee to get access to Trump's tax returns, which they could reveal to the American public by reading them into the Congressional Record from the floor of the House.
Launch investigations into the blatant corruption in Trump's Cabinet--Wilbur Ross' shady business deals and attempt to politicize the 2020 census, Ryan Zinke's ethics charges and politicization of offshore drilling decisions, Ben Carson's hiring of family members, and Betsy DeVos' connections to private prisons, Mnuchin's travel and ties to the banks and Wall Street--there is literally no end to this work.
Investigate Devin Nunes' treasonous activities.
Re-open the Intelligence Committee's Russia investigation, hold public hearings with the Trump Gang under oath, subpoena Trump's Deutsche Bank records, and expand it to include Russian interference in the 2018 election.
Protect Rod Rosenstein and Robert Mueller.
Hold floor votes on common-sense gun control, immigration reform, tax reform that favors the 99%,, Medicare for all, abolishing ICE, universal college tuition, the environment, DACA and other votes that the Republicans have been purposefully avoiding for years. None of these bills will survive Trump's veto, but GOP members of Congress will finally be on record on these issues, which will be vital in the Democrats' to increase their margins in Congress and remove Trump (kicking and screaming, no doubt) from the White House.