Simply sending the default 404 will not hurt you, I can confirm that by having removed an entire section of my site and watched the remaining pages climb in rank/traffic. Having less low quality pages is definitely the way to go right now.
Tip: look at your analytics over the past 30-90 days and find pages that receive less than a visitor per day on average from search and no direct traffic. If these pages have little to no incoming links consider removing them and/or merging them to similar content pages via 301. You'll remove low quality pages(as determined by Google) and bolster existing pages. "is this a great article?" if the answer is no or you're on the fence, ditch it. If the answer is yes build backlinks to it or merge it asap.