One of the disadvantages of a solitary religious practice, for me, is the tendency to focus on–well, solitary religious practices!
In saying that, I don’t mean to disparage solitary practice. I’ve always found my personal devotions to be the most meaningful part of my religious practice–even with regard to those gods I worship in a group setting, I feel a greater connection with deity during daily devotional practice than I do during larger group worship. So I am pretty sure that it’s the festival format rather than the number of people involved that determines that intensity of experience.
What I am not saying here is that daily devotions are more important than festivals. Daily practices can be direct, they can be personalized. A festival–or a ritual celebrated in the context of a festival–is simply going to be less intimate.
However, in a group setting there are other aspects of the religious experience that can make up for the relative lack of intimacy–worshipping with others can add a lot of energy to a ritual, and having different people with their different ways of relating to deity all together can be a very powerful thing.
Celebrating a festival–a less directly personal worship format–on your own is a little different. I freely admit that I don’t do as many festivals as I could (should?), and that is at least partly a function of being solitary. If you’re working out a festival calendar with a group, you’re likely to be working with the needs of many. If you have among your number people devoted to Dionysos, Athena, Poseidon and Artemis, you’re going to have festivals for at least all of those deities. You’re more likely to have a certain balance in your ritual year, while as a solitary worshipper you may well be skewed in the direction of your own individual direction–and there is nothing wrong with that but it is going to be a different sort of ritual year.
But in a group you are also going to have the strengths and the experiences of many to draw upon in creating and performing ritual. Depending on who is part of your group, you may have different people willing and/or able to take charge of different festivals for different gods. It can make for a remarkably rich and varied festival cycle and that can be very exciting even if it does lack the intimacy of one-on-one devotional contact.
One of the issues with celebrating festivals as a solitary worshipper is that without the intimacy and directness of personal devotions, and without the broader scope and increased energy of a group ritual, you may feel that the end experience is somehow weaker. There isn’t really an easy fix for this. But there are other ways of finding the strength and importance of an experience–and it may be a matter of trial and error before you find one that works well for you. Maybe you (or your gods) are in the “just do it” camp and you find that simply having done the ritual provides its own spiritual reward. Maybe you can find an online community to worship with, together but apart. Maybe, for you, simple is best and marking the festival day in a less elaborate fashion is ideal. Maybe you even find that a focus on personal devotion to the exclusion of all else is what suits you and your gods.
In religion, one size does not fit all.