Nemtsov had no influence on the majority of Russians and that's the reality. He was well known in the 90s when he was close to Yeltsin but that was long time ago and for most Russians that time and that government will be forever associated with all the negative things that happened to the country and its citizens since the Soviet Union fell apart. For Putin, dead Nemtsov is actually a much bigger problem, because it gives his enemies, in and outside of the country, a stick to beat him with. Those protest marches Nemtsov and other opposition leaders organized in Moscow and few other cities were, for the most part, nothing, but a minor annoyance for the government. At the height of the opposition activity back in 2012 those protests would have had close to a 150,000 - 200,000 participants at the most, but those were not just Nemtsov supporters, but rather a gathering of various groups with different ideologies, from liberals to ultra nationalists and the only common ground they had was their negative attitude towards Putin's regime.
But since then the opposition movement fell apart and nowadays those marches are barely worth a mention. Like I said, it makes absolutely no sense for Putin to get rid of Nemtsov, especially in such a blatant display, right in the center of Moscow. If it's a political assasination and everyone assumes it is, it's done by those who want to hurt Putin or at least weaken his position. It may be a result of a power struggle inside Kremlin hierarchy, could be a plan to undermine Putin and weaken his position by those who want to take over. Who knows.
Last, but not least. Regardless of my feelings towards Nemtsov as a politician, I feel genuinely sorry about his death and my deepest sympathies are with his family. I hope those guilty of the crime are found and we'll find out the truth behind it. R.I.P.
