Not sure Sinclair was overpriced at £6m; he just was never good enough for us. Rodwell at £15m possibly was overpriced, but his career has been badly curtailed by injury so it's hard to judge. He certainly had potential when we signed him. Regardless, I don't think either of those deals are relevant to Berahino. Doubt we'll take a punt on him though.
Rodwell was generally very good when he played under Mancini; MOTM against Chelsea plus two goals against Norwich towards the end of the season. Pellegrini just didn't use him, despite him being fit for the majority of his second season; people might point towards his underwhelming form for Sunderland as vindication of his 'flop' label but a year inactive is difficult to overcome unless you're mentally strong, which by all accounts Rodwell isn't. To kickstart his career, he probably needs to revert back to being a central defender; he's got all the tools to do very well there. We got most of the money we spent on him back anyway...
Barry was great value for £12m. Johnson was a good impact player, especially in our title winning season of 2011/12 and another one that we didn't really make a loss on. Lescott and Milner were possibly slightly overpriced, but both contributed positively in our transition from wealthy club to successful one. Joe Hart was the best bit of business this club has ever done, and if Delph can get/stay fit then the £8m outlay there is going to prove to be another bargain, even if just for a talented squad player.
Look at United, Spurs and Liverpool's outlays on foreign imports in the past few years; very few have proven to be good investments and the majority have flopped. Spurs have replaced expensive foreign duds like Soldado, Paulinho and Capoue with Kane, Dier, Mason and Alli and have reaped the benefits.
Mourinho has spent over £40m on Baba Rahman and Felipe Luis in the past 18 months, and the best leftback in the league in that time has arguably been Ryan Bertrand, who he sold for £12m.
The perception that English players aren't good enough or are too expensive is ignorant and naive; we had 5 of them starting when we smashed a decent United team 6-1.