I think video marketing services can work, they utilise their knowledge and experience of video marketing to give you the whole shabang and do a lot of the promotion for you, they can do updates of the marketing as time passes based on your new content etc so it is worth it but I think the majority purchasing them services will be businesses who are selling a product and want articles written about the product, websites and all sorts so they can come costly and if its for a personal channel that wont be recovering the costs then its best to think about it first. Its a field of work that I am VERY interested in doing business in myself some day.
I would stay away from any offering guaranteed views/subscribers as in 500 subscribers = $10 etc those are likely dead accounts automatically subscribing to you and wont give you views and will not share your content.
If by applications you mean sites where you watch each others videos for coins or whatever then it can work to help you get views and it can help you gain an audience if you find people on them who continue watching your videos afterwards but it is something that many dont recommend, according to the Google/Youtube TOS any kind of "gaming" of statistics is a breach of their terms which technically includes doing sub for sub, like for like or using any other similar tactics to try and get more views. I know using videos with Adsense enabled on those kinds of sites is begging to be banned, Adsense have been unfair on innocent users and its one account per life and it isnt worth the risk so if you do ever choose to use such sites I recommend you disable your ads on the videos you show on them just to be safe. It is really up to yourself whether or not to use these sorts of sites, some people frown on others for it and others like myself dont care and think its your own choice but you could be playing with fire. The biggest issue I see with these sorts of sites is that most people are on them for themselves and many will just subscribe in hope to get a sub in return.