LinkedIn (LNKD) new premium service is doing more than increasing revenues for the subscription site — it’s increasing stock prices, too.Sales Navigator lets paying users contact anyone via InMail — even people outside their network — and search LinkedIn’s database by seniority, function, industry, company and location. The service also lets you integrate LinkedIn with Salesforce, see who’s viewed your profile, and see more profiles when you search.The new tool (a great retention tactic, by the way) is expected to generate $600 million in five years.But it also led financial analysts to increase price targets on LinkedIn’s shares to $140 from $115. Apparently, subscription revenues and retention tactics that make your site more robust and pay-worthy are great for Wall Street as well.