As one of Aer Lingus' major rivals, Ryanair by virtue of their large minority shareholding will have been able to significantly influence the future of Aer Lingus, if only by virtue that they had an effective power of veto on any merger / takeover involving EI. Power to significantly events around a major rival has a value to which it is difficult to ascribe a price
The reality is that Ryanair never significantly, or even insignificantly influenced the future of Aer Lingus. Apart from IAG nobody else has/ever had any interest in buying/merging with it and that's happening only now when the long-running pensions problem has finally been resolved and the cost-reduction processes have been well advanced. Prior to that nobody would have touched them with a bargepole.
The only entity that significantly influenced the future of Aer Lingus were their unions who, time after time, significantly curbed or stalled and delayed the changes necessary to bring it into line. It would be difficult to ascribe the price of that but it surely runs into many millions over many years and which, ironically, included the cost of the hire in of aircraft from Ryanair to keep the business going when their own staff were on strike.