I currently have 3x 1080p 27" LG IPS screens in surround (almost borderless) and absolutely love them. I used to have 3x 24's and I would never go back. I'm in university right now so I do a lot of productivity work (word docs, excel spreadsheets, paper research etc) and I have no problems with the pixel density as compared to the 24's.
Although I will admit that after using my 13 inch 1080p laptop, the desktop screens are noticeably more pixelated
I personally value the extra screen real estate much much more. As for gaming, you won't notice much of a difference in pixel density between the two, but the size will give you a massive boost in utility and fun.
However I will say that I'm using very high quality factory calibrated IPS screens (they have a decent response rate - but are absolutely worth it for photoshoping and video editing), so they look great just from the color and vibrance. If you get a low-end TN panel, the 27" might lose some of its appeal.