PhD from IGNOU is as valuable as from any other university. The UGC has recently ruled that PhD from distance education is no longer valid. This is applicable to every university.
PhD is valid only in regular mode. This can be both part-time or full-time. IGNOU offers both so yes PhD from IGNOU is valuable. In fact, it is more valuable than the same degree from Manipal or Lovely Professional University.
PhD from IGNOU is valuable because of the following reasons:
Affordable fees
Both part-time and full-time available ( both approved by UGC)
Easy distance education
Can be pursued alongside a business or profession.
What really matters is what you learn during your course and how you apply it.