Andy Clough said:
Wi-fi can slow your broadband speed by up to 30% so yes, adding homeplugs should give you a faster, more robust connection.
I'd take that survey done by Epitiro with a pince of salt, and examine who commissioned the survey - I see no reason why wifi would slow down your broadband connection (providing ur average wifi throughput is fast enough to support ur max broadband speed), and also no reason why latency would noticeably increase, unless maybe everyone in ur road is using the same default channel.
Indeed, just testing on my own router - my broadband speed (wired) is 20.6Mb/s with a latency of 45ms to my favourite call of duty server, whilst wifi broadband speed is 20.8Mb/s and a latency of 48ms. So no difference.
As to homeplug/wifi - my Dlink Wifi-n Extreme gives a transfer rate of aroung 60Mbps, my Dlink 200Mbps Homeplugs give a transfer rate around 95Mbps. The wifi rate might be higher - but the wifi-n on my laptop is not mimo.
To get full speed between devices I use a gigabit switch connected to the homeplug. The homeplugs are just used to extend the network so the router can dish out dhcp addresses, devices connected to the switch can communicate to each other at full 1Gbps.